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Every year about two million people visit Mount Rushmore, were the faces of four U.S presidents were carved in granite by sculptor Gutzon Borglum and his son, the late Lincoln Borglum. The creation of the Mount Rushmore monument Line took 14 years – from 1927 to 1941 – and nearly a million dollars. There were times when money was difficult to come by and many people were jobless. To move more than 400,000 tons of rock, Borglum hired laid-off workers from the closed-down mines in the Black Hills area. He taught these men to dynamite, drill, carve, and finish the granite as they were hanging in midair in his specially devised chairs, which had many safety features. Borglum was proud of the fact that no workers were killed or severely injured during the years of blasting and carving.
During the carving, many changes in original design had to be made to keep the carved heads free of large fissures that were uncovered. However, not all the cracks could be avoided, so Borglum concocted a mixture of granite dust, white lead, and linseed oil to fill them.
Every winter, water from melting snows gets into the fissures and expands as it freezes, making the fissures bigger. Consequently, every autumn maintenance work is done to refill the cracks. The repairers swing out in space over a 500-foot drop and fix the monument with the same mixture that Borglum used to preserve this national monument for future generations.

The men who Borglum hired were      

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 The story of gold is an adventure involving kings, queens, pirates, explorers, conquerors, and the native peoples they conquered. Throughout history, gold has woven a magic spell over those it touched. Gold is beautiful and rare; a soft shiny metal that can be moulded into many (1)...... . It has been used for money, jewelry, and to decorate special buildings such as palaces and places of worship. (2)......the precious metal was discovered, prospectors rushed to mine it, starting new cities and countries as they went. Gold and the people who love it have helped shape the world we live (3).........today. Gold is one of many elements, or substances that cannot be changed by normal chemical means, that are found in the Earth's crust. Gold has a warm, sunny colour and (4)......... it does not react with air, water, and most chemicals, its shine never fades. In its natural (5)........... , gold is soft and easily shaped. When heated to 1,062 Celsius it melts and can be poured into moulds to form coins, gold bars, and other objects. Stories have been told, movies made and legends bom about the discovery of the world’s great gold deposits. It is a saga of dreams, greed, ambition and exploration.
(2)...................................

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George Washington Carver showed that plant life was more than just food for animals and humans. Carver’s first step was to analyze plant parts to find out what they were made of. He then combined these simpler isolated substances with other substances to create new products.
The branch of chemistry that studies and finds ways to use raw materials from farm products to make industrial products is called chemurgy. Carver was one of the first and greatest chemurgists of all time. Today the science of chemurgy is better known as the science of synthetics. Each day people depend on and use synthetic materials made from raw materials. All his life Carver battled against the disposal of waste materials and warned of the growing need to develop substitutes for the natural substances being used up by humans.
Carver never cared about getting credit for the new products he created. He never tried to patent his discoveries or get wealthy from them. He turned down many offers to leave Tuskegee Institute to become a rich scientist in private industry. Thomas Edison, inventor of the electric light, offered him a laboratory in Detroit to carry out food research. When the United States government made him a collaborator in the Mycology and Plant Disease Survey of the Department of Agriculture, he accepted the position with the understanding that he wouldn’t have to leave Tuskegee. As an authority on plant diseases – especially of the fungus variety – Carver sent hundreds of specimens to the United States Department of Agriculture. At the peak of his career, Carver’s fame and influence were known on every continent.

According to the passage, chemurgical can be defined as the

Choose the word or phrase that best fits each space in the following passage

 Many people love boats. Going out on the water on a warm summer day is a lot of fun. (1) _______ ,different people like different kinds of boats. Two of the most popular kinds of boat are sailboats and speedboats. Sailboats use the (2) _______to give them power. They only have small engines. In contrast, speedboats have large engines and go very fast. Furthermore, speedboats are usually not as (3) _______ as sailboats. Speedboats are small so that they can go fast. Sailboats, on the other hand, are big so that they are more comfortable. ( 4) _______, sailboats can travel into the ocean, but this would be very dangerous in a speedboat. You can only use speedboats on rivers or lakes.

(4) _______

Are organically grown foods the best food choices? The advantages claimed for such foods over conventionally grown and marketed food products are now being debated. Advocates of organic foods - a term whose meaning varies greatly - frequently proclaim that such products are safer and more nutritious than others.
The growing interest of consumers in the safety and nutritional quality of the typical North American diet is a welcome development. However, much of this interest has been sparked by sweeping claims that the food supply is unsafe or inadequate in meeting nutritional needs.
Although most of these claims are not supported by scientific evidence, the preponderance of written material advancing such claims makes it difficult for the general public to separate fact from fiction. As a result, claims that eating a diet consisting entirely of organically grown foods prevents or cures disease or provides other benefits to health have become widely publicized and form the basis for folklore.
Almost daily the public is besieged by claims for “no-aging” diets, new vitamins, and other wonder foods. There are numerous unsubstantiated reports that natural vitamins are superior to synthetic ones, that fertilized eggs are nutritionally superior to unfertilized eggs, that untreated grains are better than fumigated grains, and the like.
One thing that most organically grown food products seem to have in common is that they cost more than conventionally grown foods. But in many cases consumers are misled if they believe organic foods can maintain health and provide better nutritional quality than conventionally grown foods. So there is real cause for concern if consumers, particularly those with limited incomes, distrust the regular food supply and buy only expensive organic foods instead.

The “welcome development” mentioned in line 6 is an increase in ..........

Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage:

"Quite apart from the economic similarity between present-day automation and the mechanization which has been proceeding for centuries, it must also be stressed that even in the United States automation is by no means the only factor (1)….. people from existing jobs.
 The increasing number of unneeded workers in (2)…. years has been the result of much more simple and old-fashioned influences: farm labourers have been (3)…. out of work by bigger tractors, miners by the cheapness of oil, and railwaymen by better roads.
 It is quite wrong, therefore, to think of automation as some new monster whose arrival (4)…. the existence of employment in the same way that the arrival of myxomatosis threatened the existence of the rabbit. Automation is one (5)….. of technological change, which itself is only one of the several changes (changes in tastes, changes in social patterns, changes in organization) which (6)…. in certain jobs disappearing and certain skills ceasing to be required. And even in America, which has a level of technology and output per (7)…. much in (8)….. of Britain’s, there is no (9)…. that the (10)….  of change is actually speeding up.
 Nevertheless changes in the amount of labour needed to produce a certain output are proceeding fairly rapidly in America - and in other countries - and my proceed more rapidly in future. Indeed it is one of the main objects of economic policy."

8. which has a level of technology and output per (7)…. much in (8)….. of Britain’s, 

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What geologists call the Basin and Range Province in the United States roughly coincides in its northern portions with the geographic province known as the Great Basin. The Great Basin is hemmed in west by the Sierra Nevada and on the east Line by the Rocky Mountains; it has no outlet to the sea. The prevailing winds in the Great Basin are from the west. Warm, moist air from the Pacific Ocean is forced upward as it crosses the Sierra Nevada. At the higher altitudes it cools and the moisture it carries is precipitated as rain or snow on the western slopes of the mountains. That which reaches the Basin is air wrung dry of moisture. What little water falls there as rain or snow, mostly in the winter months, evaporates on the broad, flat desert floors. It is, therefore, an environment in which organisms battle for survival. Along the rare watercourses, cottonwoods and willows eke out a sparse existence. In the upland ranges, pinion pines and junipers struggle to hold their own.
But the Great Basin has not always been so arid. Many of its dry, closed depressions were once filled with water. Owens Valley, Panamint Valley, and Death Valley were once a string of interconnected lakes .The two largest of the ancient lakes of the Great Basin were Lake Lahontan and Lake Bonneville. The Great Salt Lake is all that remains of the latter, and Pyramid Lake is one of the last briny remnants of the former. There seem to have been several periods within the last tens of thousands of years when water accumulated in these basins. The rise and fall of the lakes were undoubtedly linked to the advances and retreats of the great ice sheets that covered much of the northern part of the North American continent during those times.
Climatic changes during the Ice Ages sometimes brought cooler, wetter weather to mid latitude deserts worldwide, including those of the Great Basin. The broken valleys of the Great Basin provided ready receptacles for this moisture.

Why does the author mention cottonwoods and willows?

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Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses. On a basic level, we can say that life is ordered. Organisms have an enormously complex organization. We're all familiar with the intricate systems of the basic unit of life, the cell. Life can also "work." Living creatures can take in energy from the environment. This energy, in the form of food, is transformed to maintain metabolic processes and for survival. Life grows and develops. This means more than just replicating or getting larger in size. Living organisms also have the ability to rebuild and repair themselves when injured. Life can reproduce. Think about the last time you accidentally stubbed your toe. Almost instantly, you moved back in pain. Finally, life can adapt and respond to the demands placed on it by the environment. There are three basic types of adaptations that can occur in higher organisms.
Reversible changes occur as a response to changes in the environment. Let's say you live near sea level and you travel to a mountainous area. You may begin to experience difficulty breathing and an increase in heart rate as a result of the change in altitude. These symptoms go away when you go back down to sea level. Body-related changes occur as a result of prolonged changes in the environment. Using there previous example, if you were to stay in the mountainous area for a long time, you would notice that your heart rate would begin to slow down and you would begin to breath normally. These changes are also reversible. Genotypic changes (caused by genetic mutation) take place within the genetic makeup of the organism and are not reversible. An example would be the development of resistance to pesticides by insects and spiders.

Which type of living creatures can adapt to the changes in the environment?

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“ Calcite- containing dust particles blow into the air and combine with nitric acid in polluted air from factories to form an entirely new particle – calcium nitrate , ” said Alexander Laskin, a senior research scientist at the Department of Energy’s Pacific Northwest National Laboratory in Richland, Washington .These nitrates have optical and chemical properties that are completely different from those of the originally dry dust particles . Due to this, climate models need to be updated to reflect this chemistry. Calcite dust is common in arid areas such as Israel, where scientists collected particles for analysis.
Working from a mountaintop, the team collected dust that had blown in from the northern shores of Egypt, Sinai,and southern Israel. The particles had combined with air containing pollutants that came from Cairo.They analyzed nearly 2,00 individual particles and observed the physical and chemical changes at the W.R Wiley Environmental Sciences Laboratory.
A key change in the properties of the newly formed nitrate particles is that they begin to absorb water and retain the moisture .These wet particles can scatter and absorb sunlight-presenting climate modelers, who need to know where the energy is going , a new wild card to deal with . Companion studies of dust samples from the Sahara and the Saudi coast and loess from China show that the higher the calcium in the mineral , the more reactive they are in with nitric acid .And once the particle is changed , it stays that way.
“When dust storms kick up these particles and they enter polluted areas , the particles change ,” Laskin said . “To what extent this is happening globally, as more of the world becomes industrialized , we don’t know . But now we have the laboratory and field evidence that shows it is definitely happening . The story is much more complicated than anybody thought .”

What is the main idea of the passage ?

Millions of people are using cellphones today. In many places, it is actually considered unusual not to use one. In many countries, cellphones are very popular with young people. They find that the phones are more than a means of communication - having a mobile phone shows that they are cool and connected.
The explosion in mobile phone use around the world has made some health professionals worried. Some doctors are concerned that in the future many people may suffer health problems from the use of mobile phones. In England, there has been a serious debate about this issue. Mobile phone companies are worried about the negative publicity of such ideas. They say that there is no proof that mobile phones are bad for your health.
On the other hand, medical studies have shown changes in the brain cells of some people who use mobile phones. Signs of change in the tissues of the brain and head can be detected with modern scanning equipment. In one case, a traveling salesman had to retire at young age because of serious memory loss. He couldn't remember even simple tasks. He would often forget the name of his own son. This man used to talk on his mobile phone for about six hours a day, every day of his working week, for a couple of years. His family doctor blamed his mobile phone use, but his employer's doctor didn't agree.
What is it that makes mobile phones potentially harmful? The answer is radiation. High-tech machines can detect very small amounts of radiation from mobile phones. Mobile phone companies agree that there is some radiation, but they say the amount is too small to worry about.
As the discussion about their safety continues, it appears that it's best to use mobile phones less often. Use your regular phone if you want to talk for a long time. Use your mobile phone only when you really need it. Mobile phones can be very useful and convenient, especially in emergencies. In the future, mobile phones may have a warning label that says they are bad for your health. So for now, it's wise not to use your mobile phone too often.

The most suitable title for the passage could be  ..........

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We live in a world of tired, sleep deprived people. In his book Counting Sheep, Paul Martin - a behavioural biologist - describes a society which is just too busy to sleep and which does not givesleeping the importance it deserves.
Modern society has invented reasons not to sleep. We are now a 24/7 society where shops and services must be available all hours. We spend longer hours at work than we used to, and more time getting to work. Mobile phones and email allow us to stay in touch round the clock and late-night TV and the Internet tempt us away from our beds. When we need more time for work or pleasure, the easy solution is to sleep less. The average adult sleeps only 6.2 hours a night during the week, whereas research shows that most people need eight or even eight and a half hours' sleep to feel at their best.
Nowadays, many people have got used to sleeping less than they need and they live in an almost permanent state of 'sleep debt'.
Until the invention of the electric light in 1879 our daily cycle of sleep used to depend on the hours of daylight. People would get up with the sun and go to bed at nightfall. But nowadays our hours of sleep are mainly determined by our working hours (or our social life) and most people are woken up artificially by an alarm clock. During the day caffeine, the world's most popular drug, helps to keep us awake. 75% of the world's population habitually consume caffeine, whichup to a point masks the symptoms of sleep deprivation.
What does a chronic lack of sleep do to us? As well as making us irritable and unhappy as humans, it also reduces our motivation and ability to work. This has serious implications for society in general.
Doctors, for example, are often chronically sleep deprived, especially when they are on 'night call', and may get less than three hours' sleep. Lack of sleep can seriously impair their mood, judgment, and ability to take decisions. Tired engineers, in the early hours of the morning, made a series of mistakes with catastrophicresults. On our roads and motorways lack of sleep kills thousands of people every year. Tests show that a tired driver can be just as dangerous as a drunken driver. However, driving when drunk is against the law but driving when exhausted isn't. As Paul Martin says, it is very ironic that we admire people who function on very little sleep instead of criticizing them for being irresponsible. Our world would be a much safer, happier place if everyone, whatever their job, slept eight hours a night.

All of the following are mentioned as those whose performance is affected by 'sleep debt' EXCEPT     .

Choose the word or phrase among A, B, C or D that best fits the blank space in the following passage.

We won't have robot doctors for a long time, (1) ____ the human doctors we have now are beginning to learn on specialized artificial intelligence to help save time.

Google Deep Mind has just announced a partnership with University College London Hospital(UCLH) which will explore (2) ____ artificial intelligence to treat patients with head and neck cancers. The goal is to develop tools to automatically identify cancerous cells for radiology machines.

Currently, radiologists employ a manual process, called image (3) ____, to make CT and MRI scans and use them to create a map of the patient's anatomy with clear guidelines of where to direct the (4) ____.

Avoiding healthy areas of the head and neck requires that map to be extraordinarily detailed; typically it takes four hours to create. Google believes it can do the same job or better in one hour.

Deep Mind, Google's research arm, works primarily in deep learning, a form of artificial intelligence that learns to identify patterns from looking at large amount of data. In this case, DeepMind researchers will (5) ____ access to anonymized radiology scans from up to 700 former UCLH patients, and then feed them into (6) ____ that would process the scans to learn the visual difference between healthy and cancerous tissue.

The partnership will (7) ____ researchers to train their algorithms with highly-specialized, high- quality data, which theoretically will enable the algorithm to (8) ____ at a higher rate of success than if they had been using publicly available scans.

For those concerned about machines making health (9) ____ decisions, UCLH made it clear in a statement to the newspaper Guardian that clinicians will be in complete control of diagnoses and treatment.

DeepMind isn't the first care. Samsung Medison, the South Korean (10) ____ company's medical device arm, recently released an ultrasound machine that uses deep learning to quickly recommend whether breast tissue is cancerous or benign. The machine's algorithm was trained on 9,000 breast tissue scans, and is pending FDA approval in the US.

(7) ____

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         The Robots Are Doing the Thinking
Some robots may take care of the dishes, do your laundry, keep the house clean, or even go to the store to do your shopping. Robots that use artificial intelligence are the ones that a lot of people are holding out for. Not only will these robots be able to take care of (1)....... , but they will be able to learn as well.
There are some types of roots that already use a form of artificial intelligence called swarm intelligence. As a(n) (2) ........... of how this works, scientists have create underwater roots that will be used to repair coral reefs that have been damaged. What these robots do is work together to rebuild damaged reefs. As they (3)........ , each one knows what has been done in one area of a reef and can help build other areas or build onto something that another robot has done. Working together, the robots create a new reef that can then be (4)............to grow and thrive on its own. Amazon, the major electronic commerce company, has recently come (5).......an ingenious idea. Instead of having a package delivered to a customer via delivery truck, Amazon will send out lying drones that ill ring a package to a person’s house or delivery almost immediately.
(4)................................

Whales are the largest animals in the world, and the gentlest creatures we know. Although the whale is very huge, it is not hindered at all by its size when it is in the water. Whales have tails that end like flippers. With just a gentle flick, it can propel itself forward. The skin of a whale is so smooth that it does not create any friction that can slow the whale down. A whale’s breathing hole is located on the top of its head, so it can breathe without having to completely push its head out of the water. Whales are protected from the cold seawater by body fat that is called blubber.
Whales live in the ocean but, in terms of behaviours, they are more similar to humans than fish. They live in family groups and they even travel in groups when they have to migrate from cooler to warmer waters. The young stay with their parents for as long as fifteen years. Whales are known not to desert the ill or injured members; instead, they cradle them.
When whales are in danger, there are people who go to great lengths to help them. One such case occurred in 1988, when three young whales were trapped in the sea. It was close to winter and the sea had begun to freeze over. Whales are mammals that require oxygen from the air, so the frozen ice was a great danger to them. All they had then was a tiny hole in the ice for them to breathe through. Volunteers from all over soon turned up to help these creatures. They cut holes in the ice to provide more breathing holes for the whales. These holes would also serve as guides for the whales so that they could swim to warmer waters.

According to the passage, why was the frozen ice on the sea surface a danger to whales?

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A healthy way to know a city Maybe you are staying in a city, and there is no park nearby where you can take your morning job. One of the more recent trend is to go on a running tour, but you are not leading the way. Rather, a running enthusiast (1).......   knows the best (2)..... in the city acts as your guide. You are going out for a run, but you are also being shown highlights of the city while you are doing it.
Guided running tours are a trend that seems to be catching (3)...... in quite a few of the bigger cities in the United States. New York City, Chicago, and San Francisco are just three of the major cities that  have  running  tours in (4)........... They offer these tours to individuals, groups, and even for corporate events. If you are going into a city with colleagues to attend a business meeting or a convention, what better way is there to see the city and network with others (5) .......while taking a healthy run? 
(1).......................................
 

The protozoans, minute, aquatic creatures each of which consists of a single cell of protoplasm, constitute a classification of the most primitive forms of animal life. They are fantastically diverse, but three major groups may be identified on the basis of their motility. The Mastigophora have one or more long tails, which they use to project themselves forward. The Ciliata, which use the same basic means for locomotion as the Mastigophora, have a larger number of short tails. The Sarcodina, which include amoebae, float or row themselves about on their crusted bodies.
In addition to their form of movement, several other features discriminate among the three groups of protozoans. For example, at least two nuclei per cell have been identified in the Ciliata, usually a large nucleus that regulates growth but decomposes during reproduction, and a smaller one that contains the genetic code necessary to generate the large nucleus.
Protozoans are considered animals because, unlike pigmented plants to which some protozoans are otherwise almost identical, they do not live on simple organic compounds. Their cell demonstrates all of the major characteristics of the cells of higher animals.
Many species of protozoans collect into colonies, physically connected to each other and responding uniformly to outside stimulate. Current research into this phenomenon, along with investigations carried out with advanced microscopes may necessitate a redefinition of what constitutes protozoans, even calling into question the basic premise that they have only one cell. Nevertheless, with the current data available, almost 40,000 species of protozoans have been identified. No doubt, as the technology improves our methods of observation, better models of classification will be proposed.

Where do protozoans probably live?

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Perhaps better known than the Cullinan Diamond is the Hope Diamond, a valuable and blue gem with a background of more than 300 years as a world traveler.The 112-carat blue stone later became the Hope Diamond was mined in India sometime before the middle of the seventeenth century and was first known to be owned by Shah Jahan, who built the Taj Mahal in memory of his beloved wife. From India, the celebrated blue stone has changed hands often, moving from location to location in distant corners of the world.
In the middle of the seventeenth century, a trader from France named Jean Baptiste Tavernier acquired the large blue diamond, which was rumored to have been illegally removed from a temple Tavemier returned to France with the big blue gem, where the stone was purchased by the Sun King Louis XIV. Louis XIV had it cut down from 112 to 67 carats to make its shape symmetrical and to maximize its sparkle. The newly cut diamond, still huge by any standards, was passed down through the royal family of France, until it arrived in the hands of Louis XVI and Marie Antoinette.
During the French Revolution, Louis XVI and his wife met their fate on the guillotine in 1793, and the big blue diamond disappeared from public sight.
The diamond somehow managed to get from France to England, where banker Henry Hope purchased it from a gem dealer early in the nineteenth century. The huge blue stone was cut into a 45.5-carat oval, and at this point it took on the name by which it is known today. The diamond stayed in the Hope family for around a century, when deep indebtedness brought on by a serious gambling habit on the part of one of Henry Hope's heirs forced the sale of the diamond.
From England, the Hope Diamond may have made its way into the hands of the Sultan of Turkey; whatever route it took to get there, it eventually went on to the United States when American Evelyn Walsh McLean purchased it in 1911. Mrs.
McLean certainly enjoyed showing the diamond off guests in her home were sometimes astounded to notice the huge stone embellishing the neck of Mrs. McLean’s Great Dane as the huge pet trotted around the grounds of her Washington, D.C. home. The Hope Diamond later became the property of jeweler Harry Winston, who presented the stunning 45.5- carat piece to the Smithsonian in 1958. The Hope Diamond is now taking a well-earned rest following its rigorous travel itinerary and is on display at the Smithsonian Institution in Washington, D.C., where it has been since 1958.

The main idea of this passage is that the Hope Diamond

Read the passage and choose the best answers:

In the United States and Canada, it is very important to (1)___________ a person directly in the eyes when you are having a conversation with him or her. If you look down or to the side when the other person is talking, that person will think that you are not interested in (2)___________ he or she is saying. This, (3) __________is not polite. If you look down or to the side when you are talking, it might seem that you are not honest.

However, people who are speaking will sometimes look away for a few seconds when they are thinking or (4)______________ to find the right word. But they always turn immediately back to look the listener directly in the eyes. These social "rules" are (5)___________ for two men, two women, a man and a woman, or an adult and a child.

(3)___________

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Geothermal energy is natural heat from the interior of the Earth that is converted to heat buildings and generate electricity. The idea of harnessing Earth’s internal heat is not new. As early as 1904 , geothermal power was used in Italy . Today, Earth’s natural internal heat is being used to generate electricity in 21 countries , including Russia, Japan, New Zealand, Iceland, Mexico, Ethiopia, Guatemala, EI Salvador, the Philippines, and the United States .Total worldwide production is approaching 9,000 MW (equivalent to nine large modern coal-burning or nuclear power plants)-double the amount in 1980 .Some 40 million people today receive their electricity from geothermal energy at a cost competitive with that of other energy sources. In EI Salvador , geothermal energy is supplying 30% of the total electric energy used.
However, at the global level, geothermal energy supplies less than 0,15%of the total energy supply.
Geothermal energy may be considered a nonrenewable energy source when rates of extraction are greater than rates of natural replenishment. However, geothermal energy has its origin in the natural heat production within Earth , and only a small fraction of the vast total resource base is being utilized today. Although most geothermal energy production involves the tapping of high heat sources, people are also using the low-temperature geothermal energy of groundwater in some applications.

Geothermal Systems
The average heat flow from the interior of the Earth is very low, about 0,06% W/m2.This amount is trivial compared with the 177 W/m2from solar heat at the surface in the United States. However, in some areas, heat flow is sufficiently high to be useful for producing energy . For the most part, areas of high heat flow are associated with plate tectonic boundaries. Oceanic ridge systems (divergent plate boundaries) and areas where mountains are being uplifted and volcanic island arcs are forming (convergent plate boundaries) are areas where this natural heat flow is anomalously high. One such region is located in the western, United States, where recent tectonic and volcanic activity has occurred.
On the basis of geological criteria, several types of hot geothermal systems (with temperatures greater than about 800C , or 1760F)have been defined, and the resource base is larger than that of fossil fuels and nuclear energy combined. A common system for energy development is hydrothermal convection, characterized by the circulation of steam and / or hot water that transfers heat from depths to the surface.

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Vitamins, taken in tiny doses, are a major group of organic compounds that regulate the mechanisms by which the body converts food into energy. They should not be confused with minerals, which are inorganic in their makeup. Although in general the naming of vitamins followed the alphabetical order of their identification, the nomenclature of individual substances may appear to be somewhat random and disorganized. Among the 13 vitamins known today, five are produced in the body. Because the body produces sufficient quantities of some but not all vitamins, they must be supplemented in the daily diet. Although each vitamin has its specific designation and cannot be replaced by another compound, a lack of one vitamin can interfere with the processing of another. When a lack of even one vitamin in a diet is continual, a vitamin deficiency may result.
The best way for an individual to ensure a necessary supply of vitamins is to maintain a balanced diet that includes a variety of foods and provides adequate quantities of all the compounds. Some people take vitamin supplements, predominantly in the form of tablets. The vitamins in such supplements are equivalent to those in food, but an adult who maintains a balanced diet does not need a daily supplement. The ingestion of supplements is recommended only to correct an existing deficiency due to unbalanced diet, to provide vitamins known to be lacking in a restricted diet, or to act as a therapeutic measure in medical treatment. Specifically, caution must be exercised with fat-soluble substances, such as vitamins A and D, because, taken in gigantic doses, they may present a serious health hazard over a period of time.

The author implies that foods

No educational medium better as means of spatial communication than the atlas. Atlases deal with such invaluable information as population distribution and density. One of the best, Pennycooke's World Atlas, has been widely accepted as a standard owing to the quality of its maps and photographs, which not only show various settlements but also portray them in a variety of scales. In fact, the very first map in the atlas is a cleverly designed population cartogram that projects the size of each country if geographical size were proportional to population. Following the proportional layout, a sequence of smaller maps shows the world’s population density, each country’s birth and death rates, population increase or decrease, industrialization, urbanization, gross national product in terms of per capita income, the quality of medical care, literacy, and language. To give readers a perspective on how their own country fits in with the global view, additional projections depict the world's patterns in nutrition, calorie and protein consumption, health care, number of physicians per unit of population, and life expectancy by region. Population density maps on a subcontinental scale, as well as political maps. Convey the diverse demographic phenomena of the world in a broad array of scales.

What is the main topic of the passage?