Each sentence has a mistake. Find it bychosing A B C or D

Man is constant destroying the natural resources which keep him alive

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The plants which ................ in the living room need a lot of water.

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Alfred Bernhard Nobel, a Swedish inventor and philanthropist, left most of his vast fortune in trust as a fund from which annual prize could be awarded to individuals and organizations that had achieved the greatest benefit to humanity in a particular year. Originally, there were six classifications for outstanding contributions designated in Nobel’s will including chemistry, physics or medicine, literature, and international peace.
The prizes are administered by the Nobel Foundation in Stockholm. In 1969, a prize for economics endowed by the Central Bank of Sweden was added. Candidates for the prizes must be nominated in writing by a qualified authority in the field of competition Recipients in physics, chemistry, and economics are selected by the Royal Swedish Academy of Sciences; in physiology or medicine by  the Caroline Institute; in literature by the Swedish Academy; and in peace by the Norwegian Nobel committee appointed by Norway’s parliament. The prizes are usually presented in Stockholm on December 10, with the King of Sweden officiating, an appropriate tribute to Alfred Nobel on the anniversary of his death. Each one includes a gold medal, a diploma, and a cash award of about one million dollars.

The word “one” in the second paragraph refers to     .

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Children’s behaviour has worsened over the past five years, according to a survey of  teachers which found that a fifth thought girls were more likely to cause trouble than boys. The survey, published after teachers at a Lancashire school went on strike over discipline, found low-level disruption, including chatting and “horsing around”, was the biggest problem. Boys were more likely to be physically aggressive while girls tended to ostracise other pupils. The behaviour of boys was more of a challenge than that of girls but the actions of each sex had deteriorated, according to 56.5% of staff surveyed by the Association of Teachers and Lecturers (ATL).  Among male pupils the most challenging behaviour for teachers was physical aggression, such as pushing, spitting, kicking and hitting. A secondary teacher quoted in the survey said boys were usually aggressive with other pupils, while girls tended to call one another names. Teachers criticised a lack of role models in the home. A primary teacher said: “The boys are far more willing to be aggressive to adults, verbally and even physically. There don’t seem to be any parental boundaries set of what is an appropriate way to speak and deal with another adult.” Teachers at Darwen Vale high school, Lancashire, walked out over unruly pupil behaviour this month. They said children challenged them to fights and threatened to film lessons and post them online. The survey of more than 850 teachers, heads and other school staff found that more than 21% thought girls’ behaviour was more challenging than boys, compared with 68% who said male pupils caused more trouble. In schools that have excluded pupils, 57% said more boys and 5% said more girls had been excluded. A department head in a primary school told the survey, carried out in March, that “classes with a majority of boys tend to be louder, less co-operative and harder to teach”. Nearly half of the staff surveyed said boys’ bravado was behind their disruption. For girls, the most likely trigger was a break-up between friends. A primary school teacher from Bedfordshire said: "Boys are generally more physical and their behaviour is more noticeable. Girls often say nasty things, which end up disrupting the lesson just as much as the boys, as other children get upset and can’t focus on their work. They are usually the ones who refuse to comply with instructions." Some staff had noticed girls’ behaviour worsening.” A teaching assistant from Weston-super-Mare said: “Girls are definitely getting more violent, with gangs of girls in school who are getting worse than the gangs of boys.” The ATL annual conference in Liverpool on Monday is due to debate a motion expressing concern at increasing numbers of girls being excluded from secondary school.  Government figures for 2008-9 showed that boys represented 78% of the total number of permanent exclusions from schools in England. This proportion was unchanged from the year before. The ATL general secretary, Mary Bousted, said: "Staff get ground down daily by the chatting and messing around, which disrupts lessons for other pupils and takes the pleasure out of teaching. Even more worrying is the physical aggression, most often among boys but also among some girls, which puts other pupils and staff at risk. Schools need to have firm and consistent discipline policies and work with parents to keep schools and colleges safe places for pupils and staff alike." The education bill, now going through the Commons, will give teachers the right to search pupils for banned items and will remove the requirement to give parents a day’s notice of detention. The education secretary, Michael Gove, said the measures in the bill would “restore discipline” in the classroom.
6. The word “which” in the last paragraph refers to _____________.

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   Family life in the United States is changing. Thirty or forty years ago, the wife was called a "housewife". She cleaned, cooked, and cared for the children. The husband earned the money for the family. He was usually out working all day. He came home tired in the evening, so he did not do much housework. And he did not see the children very much, except on weekends.

   These days, however, more and more women work outside the home. They cannot stay with the children all day. They, too, come home tired in the evening. They do not want to spend the evening cooking dinner and cleaning up. They do not have time to clean the house and do the laundry. So who is going to do the housework now? Who is going to take care of the children?

   Many families solve the problem of housework by sharing it. In these families, the husband and wife agree to do different jobs around the house, or they take turns doing each job. For example, the husband always cooks dinner and the wife always does the laundry. Or the wife cooks dinner on some nights and the husband cooks dinner on other nights.

   Then there is a question of the children. In the past, many families got help with child care from grandparents. Now families usually do not live near their relatives. The grandparents often are too far away to help in a regular way. More often, parents have to pay for child care help. The help may be a babysister or a day-care center. The problem with this kind of help is the high cost. It is possible only for couples with jobs that pay well.

   Parents may get another kind of help from the companies they work for. Many companies now let people with children work part-time. That way, parents can spend more time with their children. Some husbands may even stop working for a while to stay with the children. For these men there is a new word: They are called "househusband". In the United States more ans more men are becoming househusband every year.

   These changes in the home mean changes in the family. Fathers can learn to understand their children better, and the children can get to know their fathers better. Husbands and wives may also find changes in their marriage. They, too, may have a better understanding of each other.

These changes in the Amercan home may ______________

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Seniors in China are still highly likely to believe rumors and pseudoscience, according to reports. In recent years, China has seen more scientists and science communicators using digital platforms to combat pseudoscience, which is classified as rumors, statements, beliefs, ideas or practices that are stated as fact, but are often fabricated and scientifically untested. Despite that, many young Chinese have experienced difficulties when trying to pass on that message to older people. For example, last year, Dingxiang Doctor, a digital platform that debunks medical rumors online, released 101 articles that disproved common, inaccurate claims. However, many netizens said that when they forwarded the articles to family chat groups, they were questioned, scolded and even removed from the group by older family members. An online survey last year by Tencent, one of China’s biggest online businesses, indicated that nearly 40 percent of middle-aged and senior people had experienced online fraud, mostly related to healthcare products. Yun Wuxin, a food engineering expert who has popularized food science for more than 10 years, believes that, in general, members of the older generation lacked training in logical or critical thinking when they were young, so they have an exaggerated belief in personal experience, tradition or superstition. He said young people, especially today’s younger generation, have received better training and tend to hold skeptical or critical attitudes toward convention. He added that new media that popularize science in fresh, innovative ways － such as short videos, video blogs and animations － are very effective with young people. However, traditional methods, including television, community visits by scientists, neighborhood exhibitions and science columns in newspapers, are very important for middle-aged and elderly people who really need to understand science  
1. Which best serves as the title for the passage?

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College is usually the first time young people are on their own without parents’ guidance or rules. Students learn to participate (1) _____ a responsible member of various groups within the college environment: fellow students, roommates, teachers, college staff, sports teammates, religious groups, study groups, romantic partners or extracurricular clubs. You’ll also learn how to grow your sense of (2)_____ identity. “Socialization is a process of learning what it means to be a member of a group and navigating one’s sense of self as (3) _____ of that process. Because there are many different groups on a college (4)_____ socialization might include finding like-minded peers on campus to differentiate one’s self from others and (5) _____ closer bonds with some group members (as in fraternities and sororities),” explained Karen Sternheimer, Associate Professor of Sociology at the University of Southern California

Rewrite the sentence:
Mr. Peter drives to Amsterdam every month

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In the future, maybe all cars that run on petrol will be replaced by solar cars, which  have been around for a while, but with recent (1)__________ in solar car design and the measurement of photovoltaic cells becoming smaller, the dream of a truly efficient solar car is more reality than fantasy.  A solar car is a vehicle (2)__________ by photovoltaic cells, also called solar cells, which convert sunlight (light energy) into electrical energy.  As a source of energy on earth, there is nothing like the sun: in a mere one thousandth of one second (.001), the sun emits enough energy to fulfill our planet’s (3)_______ needs for the next 5,000 years. It is a staggering fact, and an exciting one. Since the energy from the sun is responsible for renewable resources such as wind, tides, and heat, solar energy seems to offer the brightest future for not only cars, but for the entire energy crisis. Despite the appearance that solar energy may be the least feasible among the current crop of (4)_________ fuel propositions, new solar powered devices and more specifically solar powered cars are beginning to be developed. How do solar cars work?  The photo-voltaic cells absorb photons from sunlight. This action generates heat, which the cells then convert into electrical energy and stores in an on-board battery. This process of conversion is called the photovoltaic effect. Not surprisingly, such a vehicle has zero emissions, and is very (5)________ friendly. Unfortunately, at the moment photovoltaic cells are extremely inefficient, yet as time progresses the efficiency of these cells will grow. This will make solar energy and solar cars the fuel and car of the future-a closer reality

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Esperanto is what is called a planned, or artifiial, language. It was created more than a century ago by Polish eye doctor Ludwik Lazar Zamenhof. Zamenhof believed that a common language would help to alleviate some of the misunderstandings among cultures. In Zamenhof's fist attempt at a universal language, he tried to create a language that was as uncomplicated as possible. This fist language included words such as ab, ac, ba, eb, be, and ce.This did not result in a workable language in that these monosyllabic words, though short, were not easy to understand or to retain. Next, Zamenhof tried a different way of constructing a simplified language. He made the words in his language sound like words that people already knew, but he simplifid the grammar tremendously. One example of how he simplifid the language can be seen in the suffies: all nouns in this language end in o, as in the noun amiko, which means "friend", and all adjectives end in -a, as in the adjective bela, which means "pretty". Another example of the simplifid language can be seen in the prefi mal-, which makes a word opposite in meaning;theword malamiko therefore means "enemy", and the word "malbela" therefore means "ugly" in Zamenhof's language. In 1887, Zamenhof wrote a description of this language and published it. He used a pen name, Dr. Esperanto, when signing the book. He selected the name Esperanto because this word means "a person who hopes" in his language. Esperanto clubs began popping up throughout Europe, and by 1950, Esperanto had spread from Europe to America and Asia. In 1905, the First World Congress of Esperanto took place in France, with approximately 700 attendees from 20 different countries. Congresses were held annually for nine years, and 4,000 attendees were registered for the Tenth World Esperanto Congress scheduled for 1914, when World War I erupted and forced its cancellation. Esperanto has had its ups and downs in the period since World War I. Today, years after it was introduced, it is estimated that perhaps a quarter of a million people are flent in it. This may seem like a large number, but it is really quite small when compared with the billion English speakers and billion Mandarin Chinese speakers in in today's world. Current advocates would like to see its use grow considerably and are taking  steps to try to make this happen.
7. The expression "ups and downs" pragraph 5 is closest in meaning to .....

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A satellite is best understood as a projectile, or an object that has only one force acting on it — gravity. Technically speaking, anything that crosses the Karman Line at an altitude of 100 kilometers (62 miles) is considered in space. However, a satellite needs to be going fast — at least 8 km (5 miles) a second — to stop from falling back down to Earth immediately. If a satellite is traveling fast enough, it will perpetually “fall” toward Earth, but the Earth’s curvature means that the satellite will fall around our planet instead of crashing back on the surface. Satellites that travel closer to Earth are at risk of falling because the drag of atmospheric molecules will slow the satellites down. Those that orbit farther away from Earth have fewer molecules to contend with. There are several accepted “zones” of orbits around the Earth. One is called lowEarth-orbit, which extends from about 160 to 2,000 km (about 100 to 1,250 miles). This is the zone where the ISS orbits and where the space shuttle used to do its work. In fact, all human missions except for the Apollo flights to the moon took place in this zone. Most satellites also work in this zone. Geostationary or geosynchronous orbit is the best spot for communications satellites to use, however. This is a zone above Earth’s equator at an altitude of 35,786 km (22,236 mi). At this altitude, the rate of “fall” around the Earth is about the same as Earth’s rotation, which allows the satellite to stay above the same spot on Earth almost constantly. The satellite thus keeps a perpetual connection with a fixed antenna on the ground, allowing for reliable communications. When geostationary satellites reach the end of their life, protocol dictates they’re moved out of the way for a new satellite to take their place. That’s because there is only so much room, or so many “slots” in that orbit, to allow the satellites to operate without interference. While some satellites are best used around the equator, others are better suited to more polar orbits — those that circle the Earth from pole to pole so that their coverage zones include the north and south poles. Examples of polar-orbiting satellites include weather satellites and reconnaissance satellites  
5. Which of the following is mentioned in paragraph 4 as a element that makes a satellite stay above the same spot on Earth?

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Would you believe that your diet can make a big difference in keeping a youthful appearance? It seems strange to think that the food we take in could result in fewer wrinkles. Wouldn’t it be better to put things on our skin rather than in our mouths? Well, according to one scientific theory, our bodies start aging because of oxidation. This is caused by certain oxygen-containing molecules in our cells, called free radicals. Free radicals have the capability to attach to and damage parts of our cells, including our DNA. Our bodies have the ability to repair this damage. However, as we get older, these repair mechanisms start to break down, resulting in signs of aging, such as wrinkles. Free radicals are actually produced by our bodies, but their numbers can also increase because of the food we eat. Besides avoiding foods that could potentially produce more free radicals, eating foods that contain certain vitamins and micro-nutrients can also keep us looking young. These vitamins help produce molecules called antioxidants, which actually help reduce the production of free radicals. Even better, foods containing antioxidants are not rare. Common antioxidants, like vitamins A and E, can be found in many dark-colored vegetables. For example, carrots, seaweed, spinach, and broccoli are all excellent sources of these helpful vitamins. Also, you can eat orange-colored fruits like apricots and peaches. Vitamins A and E are particularly good for helping your skin remain young-looking. These nutrients strengthen your skin and make it soft. However, if you really want to stock up quickly on nutrients that benefit your skin, you should eat cow’s liver. One small piece of cooked cow’s liver contains twice as much vitamin A as half a cup of cooked carrots.  More recently, green tea has also been tentatively added to the list of youthpromoting substances. Research on green tea’s effects on our bodies is still in the early stages. Scientists certainly believe that it is good for us, but they are cautious about predicting its ability to keep us looking youthful. However, recent experiments seem to show that green tea’s antioxidant properties can repair cell damage already sustained as well as prevent damage in the future. In fact, green tea works even better if you apply it directly to your skin as an ingredient in facial cream. “You are what you eat.” The more we find out about how our bodies work, the more this old proverb seems to be true. Think about that the next time you sit down at the table.  
4. As mentioned in the passage, the following are good foods for the skin, EXCEPT _____

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Insects’ lives are very short and they have many enemies but they must survive long enough to breed and perpetuate their kind. The less insect-like they look, the better their chance of survival. To look “inedible” by imitating plants is a way frequently used by insects to survive. Mammals rarely imitate plants, but many fish and invertebrates do. The stick caterpillar is well named. It is hardly distinguishable from a brown or green twig. This caterpillar is quite common and can be found almost anywhere in North America. It is also called “measuring worm” or “inchworm”. It walks by arching its body, then stretching out and grasping the branch with its front feet then looping its body again to bring the hind fed forward. When danger threatens, the stick caterpillar stretches its body away from the branch at an angle and remains rigid and still, like a twig, until the danger has passed. Walking sticks, or stick insects, do not have to assume a rigid, twig-like pose to find protection: they look like inedible twigs in any position. There are many kinds of walking sticks, ranging in size from the few inches of the North American variety to some tropical species that may be over a foot long. When at rest their front legs are stretched out, heightening their camouflage. Some of the tropical species are adorned with spines or ridges, imitating the thorny bushes or trees in which they live. Leaves also seem to be a favorite object for insects to imitate. Many butterflies can suddenly disappear from view by folding their wings and sitting quietly among the plants that they resemble 
2. The word “enemies” in the passage mostly means_____.

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Many of us experience multiple queues on an average day. If the move quickly,  they’re soon forgotten. But a slow line can be extremely annoying. What separated a good queuing experience from a bad one, however, is not just the speed of the line. In fact, how the wait makes us feel can have a greater impact on our perception of a queues than how much time we spend in it.  To understand how, consider the story of an airport getting complaints for the long waits at the baggage carousel. After trying fruitlessly to make baggage delivery faster, the airport simple moved the arrival gates outside of the main terminal, making people walk six times longer. Time was spent walking instead of waiting around and complaints dropped to almost zero as a result. A similar example can be observed during the postwar boom in high rise buildings in many elevator halls, where mirrors are installed to give people a chance to adjust their clothes and make sure that they look great, which distracts them from the long wait for their elevator.
For many people, the golden standard of line design and management can be found in theme parks, where waiting lines are such as integral part that companies are not afraid to invest. Some of the tricks theme parks use to make waits more bearable are hiding the line behind corners or walls to make it appear shorter and inflating the waiting times announced at each attraction. If the sign says the wait is an hour, often it will actually be more like 45 minutes, which will make people feel like they’re 15 minutes ahead of schedule. At Disneyland, designers and engineers also add games and other activities in order to give guests plenty to do, which keeps them from measuring the passage of time. According to Larson, Disney lines are so entertaining that on rainy days, when attendance is low, rides in the parks may fill up too slowly because families linger in the queue for too long.  Clever line design can also be found in supermarkets. Multiple parallel lines, each in front of a checkout, can be great if you’re in a fast one, but can feel very unfair if you’re stuck in a slow one. That’s why businesses are increasingly switching to the serpentine line, in which all customers are funneled into a single queue and then sent to the first available checkout. Compared to parallel lines, the serpentine triumphs in the key department of fairness: it’s strictly first come, first served, so no one arriving after you can be served before you
3. What can be inferred from the passage?

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For 150 years scientists have tried to determine the solar constant, the amount of solar energy that reaches the Earth. Yet, even in the most cloud-free regions of the planet, the solar constant cannot be measured precisely. Gas molecules and dust particles in the atmosphere absorb and scatter sunlight and prevent some wavelengths of the light from ever reaching the ground. With the advent of satellites, however, scientists have finally been able to measure the Sun's output without being impeded by the Earth's atmosphere. Solar Max, a satellite from the National Aeronautics and Space Administration (NASA), has been measuring the Sun's output since February 1980. Although a malfunction in the satellite's control system limited its observation for a few years, the satellite was repaired in orbit by astronauts from the space shuttle in 1984. Max's observations indicate that the solar constant is not really constant after all. The satellite's instruments have detected frequent, small variations in the Sun's energy output, generally amounting to no more than 0.05 percent of the Sun's mean energy output and lasting from a few weeks. Scientists believe these fluctuations coincide with the appearance and disappearance of large groups of sunspots on the Sun's disk. Sunspots are relatively dark regions on the Sun's surface that have strong magnetic fields and a temperature about 2,000 degrees Fahrenheit cooler than the rest of the Sun's surface. Particularly large fluctuations in the solar constant have coincided with sightings of large sunspot group. In 1980, for example, Solar Max's instrument, registered a 0.3percent drop in the solar energy reaching the Earth. At that time a sunspot group covered about 0.6 percent of the solar disk, an area 20 times larger than the Earth's surface. Long-term variations in the solar constant are more difficult to determine. Although Solar Max's data have indicated a slow and steady decline in the Sun's output, some scientists have thought that the satellite's aging detectors might have become less sensitive over the years, thus falsely indicating a drop in the solar constant. This possibility was dismissed, however, by comparing Solar Max's observations with data from a similar instrument operating on NASA's Nimbus 7 weather satellite since 1978.
8. Why did scientists think that Solar Max might be giving unreliable information?

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Most languages have several levels of vocabulary that may be used by the same speakers. In English, at least three have been identified and described. Standard usage includes those words and expressions understood, used, and accepted by a majority of the speakers of a language in any situation regardless of the level of formality. As such, these words and expressions are well defined and listed in standard dictionaries. Colloquialisms, on the other hand, are familiar words and idioms that are understood by almost all speakers of a language and used in informal speech or writing, but not considered acceptable for more formal situations. Almost all idiomatic expressions are colloquial language. Slang, refers to words and expressions understood by a large number of speakers but not accepted as appropriate formal usage by the majority. Colloquial expressions and even slang may be found in standard dictionaries but will be so identified. Both colloquial usage and slang are more common in speech than writing. Colloquial speech often passes into standard speech. Some slang also passes into standard speech, but other slang expressions enjoy momentary popularity followed by obscurity. In some cases, the majority never accepts certain slang phrases but nevertheless retains them in their collective memories. Every generation seems to require its own set of words to describe familiar objects and events. It has been pointed out by a number of linguists that three cultural conditions are necessary for the creation of a large body of slang expressions. First, the introduction and acceptance of new objects and situations in the society; second, a diverse population with a large number of subgroups; third, association among the subgroups and the majority population. Finally, it is worth noting that the terms "standard", "colloquial", and "slang" exist only as abstract labels for scholars who study language. Only a tiny number of the speakers of any language will be aware that they are using colloquial or slang expressions. Most speakers of English will, during appropriate situations, select and use three types of expressions.
9. It can be inferred from the passage that the author

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There are many strange superstitions in the world. The most common one is related to black cats, (1) ____ are the source of hundreds of unlucky superstitions. It’s a sign of bad luck (2) ____ they walk in front of you or you step on their tails. They even bring bad luck into a house if they sneeze inside! This superstition dates (3) ____ to the Middle Ages when they became associated with witches and evil spirits.  Another common superstition is about walking under a ladder. A more (4) ____ explanation can be traced back to ancient Egypt. The (5) ____ Egyptians believed that the shape of the Pyramids had a special power. It was considered very bad luck to break the “power” of this shape and that’s exactly what walking under a ladder would do!  In addition, in Roman times, people (6) ____ the habit of looking at themselves in pools of water. Some believed that these reflections were in fact “glimpses of the soul”. Any disruption to the water in the pool would bring bad luck to the person looking in it. This superstition lives on with the fear of bad luck from breaking a mirror

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Some people applied for the job, but two of them were ______

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Rachel Carson was born in 1907 in Springdale, Pennsylvania. She studied biology in college and zoology at Johns Hopkins University, where she received her master's degree in 1933. In 1936, she was hired by the US Fish and wildlife service, where she worked most of her life. Carson's first book, Under the Sea Wind, was published in 1941. It received excellent reviews, but sales were poor until it was reissued in 1952. In that year, she published The Sea Around Us, which provided a fascinating look beneath the ocean's surface, emphasizing human history as well as geology and marine biology. Her language had a poetic quality. Carson consulted no less than 1,000 printed sources. She had voluminous correspondence and frequent discussions with experts in the field. However, she always realized the limitations of her non-technical readers. In 1962, Carson published Silence Spring, a book that sparked considerable controversy. It proved how much harm was done by the uncontrolled, reckless use of insecticides. She detailed how they poison the food supply of animals, kill birds, and contaminate human food. At that time, spokes men for the chemical industry mounted personal attacks against Carson and issued propaganda to indicate that her findings were flawed. However, her work was vindicated by a 1963 report of the President's Science Advisory Committee.
2. According to the passage, what did Carson primarily study at Johns Hopkins University?

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Thunderstorms, with their jagged bursts of lightning and roaring thunder, are actually one of nature’s primary mechanisms for transferring heat from the surface of the earth into the atmosphere. A thunderstorm starts when low-lying pockets of warm air from the surface of the earth begin to rise. The pockets of warm air float upward through the air above that is both cooler and heavier. The rising pockets cool as their pressure decreases, and their latent heat is released above the condensation line through the formation of cumulus clouds. What will happen with these clouds depends on the temperature of the atmosphere. In winter, the air temperature differential between higher and lower altitudes is not extremely great, and the temperature of the rising air mass drops more slowly. During these colder months, the atmosphere, therefore, tends to remain rather stable. In summer, however, when there is a high accumulation of heat near the earth’s surface, in direct contrast to the considerably colder air higher up, the temperature differential between higher and lower altitudes is much more pronounced. As warm air rises in this type of environment, the temperature drops much more rapidly than it does in winter; when the temperature drops more than 4 degrees Fahrenheit per thousand feet of altitude, cumulus clouds aggregate into a single massive cumulonimbus cloud, or thunderhead. In isolation, a single thunderstorm is an impressive but fairly benign way for Mother Earth to defuse trapped heat from her surface; thunderstorms, however, can appear in concert, and the resulting show, while extremely impressive, can also prove extraordinarily destructive. When there is a large-scale collision between cold air and warm air masses during the summer months, a squall line, or series of thunderheads, may develop. It is common for a squall line to begin when an advancing cold front meets up with and forces itself under a layer of warm and moist air, creating a line of thunderstorms that races forward at speeds of approximately forty miles per hour. A squall line, which can be hundreds of miles long and can contain fifty distinct thunderheads, is a magnificent force of nature with incredible potential for destruction. Within the squall line, often near its southern end, can be found supercells, long-lived rotating storms of exceptional strength that serve as the source of tornadoes.
3. It can be inferred from the passage that, in summer, ________

It used to be that people would drink coffee or tea in the morning to pick them up and get them going for the day. Then cola drinks hit the market. With lots of caffeine and sugar, these beverages soon became the pick-me-up of choice for many adults and teenagers. Now drink companies are putting out so-called "energy drinks." These beverages have the specific aim of giving tired consumers more energy.

One example of a popular energy drink is Red Bull. The company that puts out this beverage has stated in interviews that Red Bull is not a thirst quencher. Nor is it meant to be a fluid replacement drink for athletes. Instead, the beverage is meant to revitalize a tired consumer's body and mind. In order to do this, the makers of Red Bull, and other energy drinks, typically add vitamins and certain chemicals to their beverages. The added chemicals are like chemicals that the body naturally produces for energy. The vitamins, chemicals, caffeine, and sugar found in these beverages all seem like a sure bet to give a person energy.

Health professionals are not so sure, though. For one thing, there is not enough evidence to show that all of the vitamins added to energy drinks actually raise a person's energy level. Another problem is that there are so many things in the beverages. Nobody knows for sure how all of the ingredients in energy drinks work together.

Dr. Brent Bauer, one of the directors at the Mayo Clinic in the US, cautions people about believing all the claims energy drinks make. He says, —It is plausible if you put all these things together, you will get a good result. || However, Dr. Bauer adds the mix of ingredients could also have a negative impact on the body. —We just don't know at this point,|| he says.

(Source: —Reading Challenge 2||, Casey Malarcher & Andrea Janzen, Compass Publishing)

According to the passage, what makes it difficult for researchers to know if an energy drink gives people energy?