2. 外语
  3. People who live in heavily industrialized areas do not get as much sunlight as they should. Dust【C1】______over a city at altitud

People who live in heavily industrialized areas do not get as much sunlight as they should. Dust【C1】______over a city at altitud

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问题     People who live in heavily industrialized areas do not get as much sunlight as they should. Dust【C1】______over a city at altitudes(海拔)of between 4,000 and 8,000 feet cuts out between 20 and 50 percent of the sunlight and up to 90 percent of the ultraviolet light(紫外线). But dust is not the only thing to【C2】______about. When fuels are burned, whether in a factory, or in a home, or in the engine of a car, CO2 is given off. CO2 in the atmosphere acts as a kind of【C3】______around the earth, keeping warms in and so slowly raising the【C4】______of the earth. This could really change the climate all over the world.
    Everybody wants to have a car.【C5】______, while they are giving us so much pleasure, cars are also poisoning us. The amount of dangerous substances sent out by a car is quite【C6】______. Did you know, for example, that a hundred cars produce on【C7】______a third of a ton of CO, as well as many other【C8】______substances every day?
    Now, more and more people are realizing the importance of clean air. Schools are now teaching about the pollution problems. Scientists and engineers are trying to【C9】______new engines for cars. But what about the millions of cars already in use? Must they all be thrown away? It might be very【C10】______to change them so that they, too, are pollution-free.
    A. forge B. screen C. expensive D. floating
    E. unfortunately F. average G. poisonous H. develop
    I. temperature J. surprising K. overtaking L. essential
    M. regulation N. generously O. worry
【C10】
选项
答案C
解析 此处应为形容词。本段第4句和第5句两个问句表明，要改装现在已经投人使用的汽车以减少它们的污染很困难，花费很大，词库中只有expensive可以表达这个意思。要注意的是，词库中的essential一词放在空白处在语法和语义上也是成立的，但是如果结合上文两个问句的内容，essential就不如expensive合适了。
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