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Directions: Write a letter of complaints according to the following situation: You bought an air conditioner and had it installed the other day, but you found that the air-conditioning didn’t work when it operated. Write a letter to 1) point out the malfunction and 2) suggest some solutions. You should write about 100 words on ANSWER SHEET 2. Do not sign your own name at the end of the letter. Use "Li Ming" instead. You don’t have to write the address.
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Most people would not object to living a few years longer than normal, as long as it meant they could live those years in good health. Sadly, the only proven way to extend the lifespan of an animal in this way is to reduce its calorie intake. Studies going back to the 1930s have shown that a considerable reduction in consumption (about 50%) can extend the lifespan of everything from dogs to nematode worms by between 30% and 70%. Although humans are neither dogs nor worms, a few people are willing to give the calorie-restricted diet a try in the hope that it might work for them, too. But not many—as the old joke has it, give up the things you enjoy and you may not live longer, but it will sure seem as if you did.Now, though, work done by Marc Hellerstein and his colleagues at the University of California, Berkeley, suggests that it may be possible to have, as it were, your cake and eat it too. Or, at least, to eat 95% of it. Their study, to be published in the American Journal of Physiology—Endocrinology and Metabolism, suggests that significant gains in longevity might be made by a mere 5% reduction in calorie intake. The study was done on mice rather than people. But the ubiquity of previous calorie-restriction results suggests the same outcome might well occur in other species, possibly including humans. However, you would have to fast on alternate days.(41)__________Cancer is the uncontrolled growth of cells. For a cancer to develop efficiently, it needs multiple mutations to accumulate in the DNA of the cell that becomes the tumor’s ancestor.(42)__________A slower rate of cell division thus results in a slower accumulation of cancer-causing mutations.(43)__________Heavy water is heavy because the hydrogen in it weighs twice as much as ordinary hydrogen(it has a proton and a neutron in its nucleus, instead of just a proton). Chemically, however, it behaves like its lighter relative. This means, among other things, that it gets incorporated into DNA as that molecule doubles in quantity during cell division.(44)__________Dr Hellerstein first established how much mice eat if allowed to feed as much as they want. Then he set up a group of mice that were allowed to eat only 95% of that amount. In both cases, he used the heavy-water method to monitor cell division. The upshot was that the rate of division in the calorie-restricted mice was 37% lower than that in those mice that could eat as much as they wanted—which could have a significant effect on the accumulation of cancer-causing mutations.(45)__________[A] To stop this happening, cells have DNA-repair mechanisms. But if a cell divides before the damage is repaired, the chance of a successful repair is significantly reduced.[B] Bingeing and starving is how many animals tend to feed in the wild. The uncertain food supply means they regularly go through cycles of too much and too little food (it also means that they are often restricted to eating less than they could manage if food were omnipresent).[C] But calorie-reduction is not all the mice had to endure. They were, in addition, fed only on alternate days: bingeing one day and starving the next. So, whether modern man and woman, constantly surrounded by food and advertisements for food, would really be able to forgo eating every other day is debatable.[D] Why caloric restriction extends the lifespan of any animal is unclear, but much of the smart money backs the idea that it slows down cell division by denying cells the resources they need to grow and proliferate. One consequence of that slow-down would be to hamper the development of cancerous tumors.[E] So, by putting heavy water in the diets of their mice, the researchers were able to measure how much DNA in the tissues of those animals had been made since the start of the experiment (and by inference how much cell division had taken place), by the simple expedient of extracting the DNA and weighing it.[F] The second reason, according to Elaine Hsieh, one of Dr Hellerstein’s colleagues, is that cutting just a few calories overall, but feeding intermittently, may be a more feasible eating pattern for some people to maintain than making small reductions each and every day.[G] At least, that is the theory. Until now, though, no one has tested whether reduced calorie intake actually does result in slower cell division. Dr Hellerstein and his team were able to do so using heavy water as a chemical "marker" of the process. 43
Every second, 1 hectare of the world’s rainforest is destroyed. That’s equivalent to two football fields. An area the size of New York City is lost every day. In a year, that adds up to 31 million hectares—more than the land area of Poland. This alarming rate of destruction has serious consequences for the environment; scientists estimate, for example, that 137 species of plant, insect or animal become extinct every day due to logging. In British Columbia, where, since 1990, thirteen rainforest valleys have been clearcut, 142 species of salmon have already become extinct, and the habitats of grizzly bears, wolves and many other creatures are threatened. Logging, however, provides jobs, profits, taxes for the government and cheap products of all kinds for consumers, so the government is reluctant to restrict or control it. Much of Canada’s forestry production goes towards making pulp and paper. According to the Canadian Pulp and Paper Association, Canada supplies 34% of the world’s wood pulp and 49% of its newsprint paper. If these paper products could be produced in some other way, Canadian forests could be preserved. Recently, a possible alternative way of producing paper has been suggested by agriculturalists and environmentalists: a plant called hemp. Hemp has been cultivated by many cultures for thousands of years. It produces fiber which can be made into paper, fuel, oils, textiles, food, and rope. For many centuries, it was essential to the economies of many countries because it was used to make the ropes and cables used on sailing ships; colonial expansion and the establishment of a world wide trading network would not have been possible without hemp. Nowadays, ships’ cables are usually made from wire or synthetic fibres, but scientists are now suggesting that the cultivation of hemp should be revived for the production of paper and pulp. According to its proponents, four times as much paper can be produced from land using hemp rather than trees, and many environmentalists believe that the large-scale cultivation of hemp could reduce the pressure on Canada’s forests. However, there is a problem: hemp is illegal in many countries of the world. This plant, so useful for fiber, rope, oil, fuel and textiles, is a species of cannabis, related to the plant from which marijuana is produced. In the late 1930s, a movement to ban the drug marijuana began to gather force, resulting in the eventual banning of the cultivation not only of the plant used to produce the drug, but also of the commercial fiber-producing hemp plant. Although both George Washington and Thomas Jefferson grew hemp in large quantities on their own land, any American growing the plant today would soon find himself in prison—despite the fact that marijuana cannot be produced from the hemp plant, since it contains almost no THC (the active ingredient in the drug). In recent years, two major movements for legalization have been gathering strength. One group of activists believes that ALL cannabis should be legal—both the hemp plant and the marijuana plant—and that the use of the drug marijuana should not be an offense. They argue that marijuana is not dangerous or addictive, and that it is used by large numbers of people who are not criminals but productive members of society. They also point out that marijuana is less toxic than alcohol or tobacco. The other legalization movement is concerned only with the hemp plant used to produce fiber; this group wants to make it legal to cultivate the plant and sell the fiber for paper and pulp production. This second group has had a major triumph recently: in 1997, Canada legalized the farming of hemp for fiber. For the first time since 1938, hundreds of farmers are planting this crop, and soon we can expect to see pulp and paper produced from this new source. The author seems to imply in the passage that
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Most people would not object to living a few years longer than normal, as long as it meant they could live those years in good health. Sadly, the only proven way to extend the lifespan of an animal in this way is to reduce its calorie intake. Studies going back to the 1930s have shown that a considerable reduction in consumption (about 50%) can extend the lifespan of everything from dogs to nematode worms by between 30% and 70%. Although humans are neither dogs nor worms, a few people are willing to give the calorie-restricted diet a try in the hope that it might work for them, too. But not many—as the old joke has it, give up the things you enjoy and you may not live longer, but it will sure seem as if you did.Now, though, work done by Marc Hellerstein and his colleagues at the University of California, Berkeley, suggests that it may be possible to have, as it were, your cake and eat it too. Or, at least, to eat 95% of it. Their study, to be published in the American Journal of Physiology—Endocrinology and Metabolism, suggests that significant gains in longevity might be made by a mere 5% reduction in calorie intake. The study was done on mice rather than people. But the ubiquity of previous calorie-restriction results suggests the same outcome might well occur in other species, possibly including humans. However, you would have to fast on alternate days.(41)__________Cancer is the uncontrolled growth of cells. For a cancer to develop efficiently, it needs multiple mutations to accumulate in the DNA of the cell that becomes the tumor’s ancestor.(42)__________A slower rate of cell division thus results in a slower accumulation of cancer-causing mutations.(43)__________Heavy water is heavy because the hydrogen in it weighs twice as much as ordinary hydrogen(it has a proton and a neutron in its nucleus, instead of just a proton). Chemically, however, it behaves like its lighter relative. This means, among other things, that it gets incorporated into DNA as that molecule doubles in quantity during cell division.(44)__________Dr Hellerstein first established how much mice eat if allowed to feed as much as they want. Then he set up a group of mice that were allowed to eat only 95% of that amount. In both cases, he used the heavy-water method to monitor cell division. The upshot was that the rate of division in the calorie-restricted mice was 37% lower than that in those mice that could eat as much as they wanted—which could have a significant effect on the accumulation of cancer-causing mutations.(45)__________[A] To stop this happening, cells have DNA-repair mechanisms. But if a cell divides before the damage is repaired, the chance of a successful repair is significantly reduced.[B] Bingeing and starving is how many animals tend to feed in the wild. The uncertain food supply means they regularly go through cycles of too much and too little food (it also means that they are often restricted to eating less than they could manage if food were omnipresent).[C] But calorie-reduction is not all the mice had to endure. They were, in addition, fed only on alternate days: bingeing one day and starving the next. So, whether modern man and woman, constantly surrounded by food and advertisements for food, would really be able to forgo eating every other day is debatable.[D] Why caloric restriction extends the lifespan of any animal is unclear, but much of the smart money backs the idea that it slows down cell division by denying cells the resources they need to grow and proliferate. One consequence of that slow-down would be to hamper the development of cancerous tumors.[E] So, by putting heavy water in the diets of their mice, the researchers were able to measure how much DNA in the tissues of those animals had been made since the start of the experiment (and by inference how much cell division had taken place), by the simple expedient of extracting the DNA and weighing it.[F] The second reason, according to Elaine Hsieh, one of Dr Hellerstein’s colleagues, is that cutting just a few calories overall, but feeding intermittently, may be a more feasible eating pattern for some people to maintain than making small reductions each and every day.[G] At least, that is the theory. Until now, though, no one has tested whether reduced calorie intake actually does result in slower cell division. Dr Hellerstein and his team were able to do so using heavy water as a chemical "marker" of the process. 41
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