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A gesture is an action that sends a message from one person to another without using words. We use gestures to communicate with others. There are some gestures that have completely different meaning depending on when and where they are used.
When an American wants to show that something is OK. or good, he raises his hand and makes a circle with his thumb and foreigners. The circle sign has only one meaning for him. He might be surprised to learn that in other countries it can mean something different. In Japan, for instance, it is the gesture for money. In France, it means 'zero' or 'worthless'. Such differences can lead to all kinds of misunderstanding when foreigners meet. But why is it that the same gesture has so many different meanings?
When some people want to show that something is exact or precise, they make a sign to show that they are holding something between the tips of their thumb and forefinger. Many people from all over the world do this when they want to make a specific point as they are speaking. People later started using this signal to mean 'exactly right' or 'perfect'. This was how the famous OK was bom.
In Japan, money means coins and coins are around. Therefore, making a round hand sign came to represent money. It is simple as that. The French sign for 'nothing' or 'worthless' also has a simple origin. This time the circle doesn't represent a coin, but nought. Nought equals zero, zero equals nothing, nothing equals worthless.

What does the circle sign represent in France?

Fill in each numbered blank with one suitable word or phrase.

In 1986 Vietnam (1)_____ a political and economic innovation campaign (Doi Moi) that introduced reforms intended to facilitate the transition from a centralized economy to a “socialist-oriented market economy”. Doi Moi combined government planning with free-market incentives. The program abolished agricultural (2) _____, removed price controls on agricultural goods, and enabled farmers to sell their goods in the marketplace. It encouraged the establishment of private businesses and foreign investment, including foreign-owned (3) _____.

By the late 1990s, the success of the business and agricultural (4) _____ ushered in under Doi Moi was evident. More than 30,000 private businesses had been (5) _____, and the economy was growing at an annual rate of more than 7 percent. From the early 1990s to 2005, poverty (6) _____ from about 50 percent to 29 percent of the population. However, progress varied geographically, with most prosperity concentrated in urban areas, (7) _____ in and around Ho Chi Minh City. In general, rural areas also made progress, as rural households (8) _____ in poverty declined from 66 percent of the total in 1993 to 36 percent in 2002. (9) _____ contrast, concentrations of poverty remained in (10) _____ rural areas, particularly the northwest, north-central coast, and central highlands. Government control of the economy and a nonconvertible currency have protected Vietnam from what could have been a more severe impact resulting from the East Asian financial crisis in 1997.

(7)_____

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Footracing is a popular activity in the United States. It is seen not only as a competitive sport but also as a way to exercise, to enjoy the camaraderie of like–minded people, and to donate money to a good cause. Though serious runners may spend months training to compete, other runners and walkers might not train at all. Those not competing to win might run in an effort to beat their own time or simply to enjoy the fun an exercise. People of all ages. From those of less than one year (who may be pushed in strollers) to those in their eighties, enter into this sport. The races are held on city streets, on college campuses, through parks, and in suburban areas, and they are commonly 5 to 10 kilometers in length.
The largest footrace in the world is the 12 kilometer Bay to Breakers race that is held in San Francisco every spring. This race begins on the east side of the city near San Francisco Bay and ends on the west side at the Pacific Ocean. There may be 80,000 or more people running in this race through the streets and hills of San Francisco. In the front of are the serious runners who compete to win and who might finish in a little as 34 minutes. Behind them are the thousands who take several hours to finish. In the back of the race are those who dress in costumes and come just for fun. One year there was a group of men who dresses like Elvis Presley, and another group consisted of the firefighters who were tired together in a long line and who were carrying a firehose. There was even a bridal party, in which the bride was dressed in a long white gown and the groom wore a tuxedo. The bride and groom threw flowers to bystanders, and they were actually married at some point along the route.

The phrase “a good cause” in paragraph 1 could be best replaced by which of the following?

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.

According to the writer, people shoul .............

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Have you ever wondered what it would be like to get your dream job? It can take years to get the education and develop the skills you need for the perfect job. However, there is a way to experience your dream job without having to get the required training or degree. Since 2004, Brian Kurth’s company, Vocation Vacations, has been connecting people with mentors who have the jobs of their dreams.
Kurth had been working for a phone company before starting his own company. He didn’t like his job, and he had a long time to think about it on his drive to and from work. He also thought about his dream job while driving. He was interested in becoming a dog trainer, but he didn’t want to take any chances and switch to a field he didn’t have experience in. He really wanted to know what the job was like and if it was realistic for him to work towards his goal. So, he found a mentor – a dog trainer that could tell him about the job and everything it involved. After that, he helped his friends find mentors to explore jobs they were interested in. They thought it was helpful to talk to people who had their dream jobs before spending lots of time and money getting the training they needed for those jobs.
Kurth saw how much this helped his friends, so he decided to turn it into his business. He started Vocation Vacations in 2004, and by 2005, the company was offering experience with over 200 dream jobs. Today, about 300 mentors work with the company to share their knowledge about their jobs. Customers pay to experience the job of their dreams and work with these mentors to see what a job is really like. A “job vacation” costs between $350 and $3,000 and can be for one to three days. Many people use Vocation Vacations to see if their dream job is a career path they want to continue. Others do it just to experience the job of their dreams one time.
Vocation Vacations jobs are in the fields of fashion, food, entertainment, sports and animals. Many people want to try glamorous jobs. For example, they want to try working as actors, music producers, photographers and fashion designers. According to Kurth, some other popular dream jobs are working as bakers, hotel managers and wedding planners.

What do mentors at Vocation Vacations do?

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The pain of a migraine headache can virtually disable a person who suffers from it. Millions and millions of people suffer from migraines, although many of them do not even recognize that a migraine is different from a regular headache. A migraine is not at all the same as a normal headache, and it seems to have a very physical cause.
One symptom of a migraine is a precursor, which is a visual aura before an attack. Yet only about a third of patients actually experience that, and it is therefore not a requirement in the diagnosis. Other symptoms include increased pain when a person moves, nausea, and sensitivity to light and sound. Scientists now believe that migraines are caused, not by abnormal blood vessels as previously believed, but instead by a unique electrical disorder of brain cells. Physicians used to treat migraines with medicine to constrict blood vessels because of the belief that dilated blood vessels were the cause.
The new research has been enhanced by imaging devices that allow scientists to watch patients' brains during an attack. The results show that sufferers have abnormally excitable neurons, or brain nerve cells. Prior to the attack, the neurons suddenly fire off electrical pulses at the back of the brain, which ripple like waves on a lake after a stone hits the water. They ripple across the top and then the back of the brain, ultimately affecting the brain stem where the pain centers are located. The pain then generates possibly from the brain stem itself or from blood vessels inflamed by the rapidly changing blood flow, or perhaps from both.
Scientists have experimented by applying a powerful magnet to stimulate the neurons and discovered that some people's brains react differently than others'. When stimulation was applied to the brains of people who had suffered migraines, they saw the initial aura, and some actually suffered migraines. When the same stimulation was applied to the brains of people who had never suffered migraines, they realized no effect and the neurons showed no change.
Scientists and doctors continue to work on the research in an attempt to find the perfect treatment. It is considered important to treat migraines because it is believed that prolonged untreated attacks could cause physical changes in the brain leading to chronic pain.

The new research indicates that the neurons in the brain of migraine sufferers

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Washington was the first city in history to be created solely for the purpose of governance. Following the Revolution, members of Congress had hotly debated the question of a permanent home for themselves and for those departments – the Treasury, the Patent Office and so on – which even the sketchiest of central governments would feel obliged to establish. In 1790, largely in order to put an end to congressional bickering, George Washington was charged with selecting a site for the newly designated federal district. Not much to anyone’s surprise but to the disappointment of many he chose a tract of land on the banks of the Potomac River, a few miles upstream from his beloved plantation Mount Vernon.
The District of Columbia was taken in part from Virginia and in part from Maryland. At the time it was laid out, its hundred square miles consisted of gently rolling hills, some under cultivation and the rest heavily wooded, with a number of creeks and much swampy land along the Potomac. There is now a section of Washington that is commonly referred to as Foggy Bottom; that section bore the same nickname a hundred and eighty years ago.
Two ports cities, Alexandria and Georgetown, flourished within sight of the new capital and gave it access by ship to the most important cities of the infant nation – Charleston, Baltimore, Philadelphia, New York, Newport, Salem and Portsmouth – and also to the far-off ports of England and the Continent.

The word “hotly” in paragraph 1 is closet in meaning to     .

There are many theories about the beginning of drama in ancient Greek. The one most widely accepted today is based on the assumption that drama evolved from ritual. The argument for this view goes as follows. In the beginning human beings viewed the natural forces of the world, even the seasonal changes, as unpredictable, and they sought, through various means, to control these unknown and feared powers. Those measures which appeared to bring the desired results were then retained and repeated until they hardened into fixed rituals. Eventually stories arose which explained or veiled the mysteries of the rites. As time passed some rituals were abandoned, but the stories, later called myths, persisted and provided material for art and drama.
Those who believed that drama evolved out of ritual also argue that those rites contained the seed of theatre because music, dance, masks, and costumes were almost always used. Furthermore, a suitable site had to be provided for performances, and when the entire community did not participate, a clear division was usually made between the “acting area” and “auditorium”. In addition, there were performers, and since considerable importance was attached to avoiding mistakes in the enactment of rites. Religious leaders usually assumed that task. Wearing masks and costumes, they often impersonated other people, animals, or supernatural beings, and mimed the desired effect- success in hunt or battle, the coming rain, the revival of the Sun-as an actor might. Eventually such dramatic representations were separated from religious activities.
Another theory traces the theatre’s origin from the human interest in storytelling. According to this view, tales (about the hunt, war, or other feats) are gradually elaborated, at first through the use of impersonation, action, and dialogue by a narrator and then through the assumption of each of the roles by a different person. A closely related theory traces theatre to those dances that are primarily rhythmical and gymnastic or that are imitations of animal movements and sound.

Which of the following is NOT mentioned as a common element of theatre and ritual?

Choose the word which is stresses differently from the rest: insecticide, fertilizer, pesticide, herbicide

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What unusual or unique biological train led to the remarkable diversification and unchallenged success of the ants for over 50 million years? The answer appears to be that they were the first group of predatory eusocial insects that both lived and foraged primarily in the soil and in rotting vegetation on the ground. Eusocial refers to a form of insect society characterized by specialization of tasks and cooperative care of the young; it is rare among insects. Richly organized colonies of the land made possible by eusociality enjoy several key advantages over solitary individuals.
Under most circumstances groups of workers are better able to forage for food and defend the nest, because they can switch from individual to group response and back again swiftly and according to need. When a food object or nest intruder is too large for one individual to handle, nestmates can be quickly assembled by alarm or recruitment signals. Equally important is the fact that the execution of multiple- step tasks is accomplished in a series-parallel sequence. That is, individual ants can specialize in particular steps, moving from one object (such as a larva to be fed) to another (a second larva to be fed). They do not need to carry each task to completion from start to finish - for example, to check the larva first, then collect the food, then feed the larva. Hence, if each link in the chain has many workers in attendance, a sense directed at any particular object is less likely to fail. Moreover, ants specializing in particular labor categories typically constitute a caste specialized by age or body form or both. There has been some documentation of the superiority in performance and net energetic yield of various castes for their modal tasks, although careful experimental studies are still relatively few.
What makes ants unusual in the company of eusocial insects is the fact that they are the only eusocial predators (predators are animals that capture and feed on other animals) occupying the soil and ground litter. The eusocial termites live in the same places as ants and also have wingless workers, but they feed almost exclusively on dead vegetation.

According to the passage, one thing eusocial insects can do is rapidly switch from     .

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In the United States, friendship can be close, constant, intense, generous and real, yet fade away in a short time if circumstances change. Neither side feels hurt by this. Both may exchange Christmas greetings for a year or two, perhaps a few letters for a while - then no more. If the same two people meet again by chance, even years later, they pick up the friendship where they left off and are delighted.
In the United States, you can feel free to visit people's homes, share their holidays, or enjoy their lives without fear that they are taking on a lasting obligation. Do not hesitate to accept hospitality because you can’t give it in turn. No one will expect you to do so for they know you are far from home. Americans will enjoy welcoming you and be pleased if you accept their hospitality easily.
Once you arrived there, the welcome will be fun, warm, and real. Most visitors find themselves readily invited into many homes there. In some countries it is considered inhospitable to entertain at home, offering what is felt as only home cooked food, not doing something for your guests." It is felt that restaurant entertaining shows more respect and welcome. Or for other different reasons, such as crowded space, language difficulties, or family customs, outsiders are not invited into homes.
In the United States, both methods are used, but it is often considered friendlier to invite a person to one's home than to go to a public place, except in purely business relationship. So, if your host or hostess brings you home, do not feel that you are being shown inferior treatment.
Don't feel neglected if you do not find flowers awaiting you in your hotel room, either. Flowers are very expensive there; hotel delivery is uncertain; arrival times are delayed, changed or cancelled - so flowers are not customarily sent as a welcoming touch. Please do not feel unwanted! Outward signs vary in different lands; the inward welcome is what matters, and this will be real.A

In the United States, inviting guests to a family dinner is    than inviting them to a public place, except some situations.

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 robots that already use a form of artificial intelligence called “swarm intelligence”. As a(n) (2)___________ of how this works, scientists have created underwater robots 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 flying drones that will bring a package to a person’s house for delivery almost immediately. 

(3)__________

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Working on the computer is very tough on your body, which is not used to this modem type of work. Sitting has long been known to cause back pain and negatively influence circulation, which can promote cardiovascular disease. Extensive use of the keyboard and mouse can lead to stiffening of the muscles in your hands, arms, and neck. Staring at a bright screen for too long can cause dry eyes and headaches. So, computer work can be as unhealthy a job as you can imagine.
First and foremost, sitting for long stretches of time is a very serious health risk! Sitting affects your blood circulation, your back experiences a steady stress, you are more likely to drink and eat stuff that isn’t good for you, and you bum very little calories, making it more likely that you overeat. As a result, sitting contributes to a host of conditions, most notably gaining weight, diabetes, heart disease, cancer, and consequently a shortened life span.
Second, bad posture causes pain. You can develop bad posture from anything you do habitually, whether it’s sitting, standing, or walking. The typical consequences associated with bad posture while working on the computer are pain in the back, shoulder, and neck, often resulting in tension headaches.
Third, staring at the screen causes eve strain. Staring at a bright screen for hours can lead to eye fatigue or eye strain, headaches, blurred vision, burning, itching or tearing eyes, and temporary vision disorders. Fortunately, eye strain rarely results in a permanent condition and symptoms can be prevented or cured rather easily.
Last, but not least, emotional pressure and isolation cause anxiety and depression. Computers are very efficient tools in that they help us with getting more work done in less time. At the same time, you spend less face-to-face time with your colleagues, family, or friends. This can lead to isolation, anxiety, and depression, i.e. both physical and mental health issues. The symptoms are manifold and can include tense muscles, back pain, headaches, poor sleep (insomnia), increased or flat breathing, quickened pulse, and generally signs of stress, depression, or anxiety.

According to the passage, human body is NOT     working on the computer.

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After the Anasazi abandoned southwestern Colorado in the late 1200s or early 1300s, history’s pages are blank. The Anasazi were masons and apartment builders who occupied the deserts, river valleys, and mesas of this region for over a thousand years, building structures that have weathered the test of time.
The first Europeans to visit southwestern Colorado were the ever-restless, ambitious Spanish, who sought gold, pelts, and slaves. In 1765, under orders from the Spanish governor in Santa Fe, Juan Maria Antonio Rivera led a prospecting and trading party into the region. Near the Dolores River in southwestern Colorado, he found some insignificant silver-bearing rocks, and it is thought that it was he who named the mountains nearby the Sierra de la Plata or the Silver Mountains. Rivera found little of commercial value that would interest his superiors in Santa Fe, but he did open up a route that would soon lead to the establishment of the Old Spanish Trail. This expedition and others to follow left names on the land which are only reminders we have today that the Spanish once explored this region.
In 1776, one of the men who had accompanied Rivera, Andre Muniz, acted as a guide for another expedition. That party entered southwestern Colorado in search of a route west to California, traveling near today’s towns of Durango and Dolores. Along the way, they camped at the base of a large green mesa which today carries the name Mesa Verde. They were the first Europeans to record the discovery of an Anasazi archeological site in southwestern Colorado.
By the early 1800s, American mountain men and trappers were exploring the area in their quest for beaver pelts. Men like Peg-leg Smith were outfitted with supplies in the crossroads trapping town of Taos, New Mexico. These adventurous American trappers were a tough bunch. They, possibly more than any other newcomers, penetrated deeply into the mountain fastness of southwestern Colorado, bringing back valuable information about the area and discovering new routes through the mountains. One of the trappers, William Becknell, the father of the Santa Fe Trail, camped in the area of Mesa Verde, where he found pottery shards, stone houses, and other Anasazi remains.

In paragraph 4, the author suggests that     .

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The traditional definition of literacy is considered to be the ability to read and write, or the ability to use language to read, write, listen, and speak. In modern contexts, the word refers to reading 4 and writing at a level (1)......... for communication, or at a level that lets one understand and communicate ideas in a literate society so as to take (2)....... in that society. The United Nations Educational, Scientific and Cultural Organization (UNESCO) has drafted the following definition: “Literacy is the ability to identify, understand, interpret, create, communicate and compute, using printed and written materials associated with varying contexts. Literacy involves a continuum of learning to enable an individual to achieve his or her goals, to develop his, or her knowledge and potential, and to participate fully in the wider society.”
Many policy analysts consider literacy rates a crucial measure of a region’s human capital. This claim is made on the (3)........ that literate people can be trained less expensively than illiterate people, generally have a higher socio-economic status and enjoy better health and employment prospects. Policy makers also argue that literacy increases job opportunities and access to higher education. In Kerala, India, for example, female and child mortality rates declined (4)......... in the 1960s, when girls who were educated in the education reforms after 1948 began to raise families. Recent researchers, (5)........., argue that correlations such as, the one listed above may have more to do with the effect of schooling rather than literacy in general.
(5)..............................

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In Viet Nam festivals often take place during the three months in spring and in autumn when people have a lot of leisure time. In addition, the climate in spring and autumn is especially suitable for holding festivals and for festivals goers to enjoy. Traditional festivals constitute a form of cultural activities, a spiritual product which the people have created and developed during the course of history. From generation to generation, the Vietnamese people preserve the fine tradition of “remembering the source while drinking water.” Festivals are events which represent this tradition of the community as well as honour the holy figures named as “gods” -the real persons in national history or legendary persons. The images of gods converge the noble characteristics of mankind. They are national heroes who fought against foreign invaders, reclaimed new lands, treated people, fought against natural calamities, or those legendary characters who affect the earthly life.
Accordingly, first and foremost, festivals are events when people pay tribute to divinities that rendered merits to the community and the nation. These are occasions when people come back to either their natural or national roots, which form a sacred part in their mind. Furthermore, testivals represent the strength of the commune or village, the local region or even the whole nation. Worshipping the same god, the people unite in solidarity to overcome difficulties, striving for a happy and wealthy life.
Moreover, festivals display the demand for creativity and enjoyment of spiritual and material cultural values of all social strata. They become a form of education under which fine traditional moral values can be handed from one generation to the next in a unique way of combining spiritual characters with competition and entertainment games. Festivals are also the time people can express their sadness and worries in a wish that gods might bestow favour on them to help them strive for a better life.

What affects the time to hold festivals in Viet Nam?

Read the passage and choose the best answers:

Never say anything negative about past experiences, employers, or courses or professors. Always think of something positive about an experience and talk about that. You should also be __(1)__. If you are genuinely interested __(2)__ the job, let the interviewer know that.

One of the best ways to show you are keen on a job is to demonstrate that you have researched the organization prior to the interview. You can also __(3)__ interest by asking questions about the job, the organization, and its service and products. The best way to impress an employer is to ask questions that build your interview discussion. This shows you are interested and __(4)__ close attention to the interviewer. It is a good idea to prepare a few questions in advance, but an insightful comment based on your conversation can make an even stronger statement. At the __(5)__ of the interview, it is appropriate for you to ask when you may expect to hear from the employer.

__(5)__

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Our eyes and ears might be called transformers because they send the light and sound around us and turn them into electrical impulses that the brain can interpret. These electrical impulses that have been transformed by the eyes and ears reach the brain and are turned into massages that we can interpret. For the eye, the process begins as the eye admits light waves, bends them at the cornea and lens, and then focuses them on the retina. At the back of each eye, nerve fibers bundle together to form optic nerves, which join and then split into optic tracts. Some of the fibers cross so that part of the input from the right visual field goes into the left side of the brain, and vice versa. The process in the ear is carried out through sensory cells that are carried in fluid-filled canals and that are extremely sensitive to vibration. Sound that is transformed into electricity travels along nerve fibers in the auditory nerve. These fibers form a synapse with neurons that carry the massages to the auditory cortex on each side of the brain.

What does the word “them” in line 2 refers to?

Choose the word which is stresses differently from the rest: effect, event, emerge, even

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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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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.

What does the word “reversible” in the passage mean?