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Answer Questions by referring to the events which happened during the terms when 3 American presidents held office in the follow

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问题     Answer Questions by referring to the events which happened during the terms when 3 American presidents held office in the following article.
    A=Hydro power
    B=Nuclear power
    C=Coal-fired power
    D=Solar power
    Our demand for electricity is climbing so fast that over the next decade U.S. generating capacity must increase by a third. Fossil fuels supply nearly three-quarters of this energy. But the smoke-belching stacks of coal-fired, gas-fired and oil-fired plants are also responsible for about half of our air pollution.
    That, we used to think, is a small price to pay for progress. But there is an alternative, one that produces no smoke and can actually create more fuel than it consumes. In many regions it is even cheaper than coal-fired electricity: nuclear power.
    Already nuclear power is the second largest source of our electricity, and a new family of "failsafe" nuclear reactors—some now under construction in Japan—may one day make nuclear power even cheaper and more plentiful.
    The only major difference between nuclear and conventional plants is that nuclear fuel is far more radioactive. For this reason, the core must be sealed from the outside environment—and so must the spent fuel, which remains radioactive for year.
    If other types of power didn’t present equal or worse problems, it would make no sense to consider nuclear power at all. But they do:
    Coal is much dirtier than it used to be. The U.S. reserves of clean-burning anthracite are virtually exhausted. Today, power plants must use soft coal, often contaminated with sulfur. When the smoke from this coal is dissolved by precipitation, it results in "acid rain".
    Burning coal produces carbon dioxide as well, which can act as a blanket, trapping solar heat in our atmosphere. Eventually, this could contribute to global warming, the greenhouse effect, though there is no conclusive evidence that this has begun.
    Coal also contains a surprising amount of radioactive material. Indeed, a coal-fired electric plant spews more radioactive pollution into the air than a nuclear plant.
    Oil and natural gas are too scarce to meet our electrical needs now, let alone in the next century. We already import over 40 percent of our oil from abroad, and that will likely increase.
    Solar power seems to be a wonderful idea: Every square yard of sunshine contains about 1000 watts of inexhaustible energy, free for the taking. The trouble is, the taking isn’t free. To meet our electrical needs, we’d have to build enough collector plates to cover the state of Delaware. No serious student of solar power expects it to be anything but a supplement to conventional electricity for decades.
    Wind power generated a lot of excitement in the early 1980s, when magazines featured photographs of a "wind farm" at Altamont Pass, California, with hundreds of windmills. Everyone seemed to forget that taxpayers’ money helped buy the farm. Today, the giant blades spin productively only half a year, because winds frequently aren’t strong enough to cover costs.
    Hydro power is the cleanest practical source of electricity. But in the United States, most rivers that can be profitably dammed already are.
    Other, more exotic energy schemes would harness ocean tides and waves, nuclear fusion (the process that powers the sun) or heat from the earth’s crust or the sea. But even proponents admit that none of these will become a major source of energy soon.
    Now Let’s look at the advantages of nuclear power.
    1. It’s clean. Radioactive emissions are negligible, much less than the radioactivity released into the air naturally from the earth or produced by cosmic rays. Standing next to a nuclear plant, I am exposed to only one-half of one percent more radiation than when sitting in my living room. A coal station, on the other hand, requires huge dumps of fuel and ashes that menace the environment.
    Despite a widespread misconception, nuclear waste is not a technical problem. The 108 nuclear plants in the United States generate less than 4,000 tons of fuel waste each year. In fact, all 33 years’ worth of the nation’s spent nuclear fuel would only fill a football field to a depth of five feet. Non-nuclear hazardous waste, by contrast, totals 275 million tons annually. And nuclear waste is easy to monitor and control. The spent fuel can be kept on the premises of years until it decays to a radiation level suitable for trucking to long-term storage sites.
    2. It’s inexhaustible. The U.S. uranium reserves will last many decades, and our long-term supply is guaranteed. Through a process called "breeding", a reactor can convert uranium into plutonium—an even better fuel. Breeder reactors, now in use in France, could thus extend the reserves for millions of years.
    3. It’s secure. Because it needs so little fuel, a nuclear plant is less vulnerable to shortages produced by. strikes or by natural calamities. And since uranium is more evenly scattered about the globe than fossil fuels, nuclear power is less threatened by cartels and international crises.
    4. It’s cheap. In France, where nuclear power supplies 70 percent of the electricity, nuclear power costs 30 percent less than coal-fired power. This enables France to export electricity to its neighbors. In Canada, where nuclear power supplies 15 percent of the electricity, Ontario Hydro has proposed building ten more nuclear reactors over the next 25 years.
    Which power...
选项 A、 
B、 
C、 
答案C
解析
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