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  3. There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automob

There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automob

admin2019-05-15  107
问题    There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automobile traffic. At present, we realize that although these are the areas with the worst air pollution, the problem is literally worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the east of the United States and brought health warnings in rural areas away from any major concentration of manufacturing and automobile traffic. In fact, the very climate of the entire earth may be infected by air pollution. Some scientists consider that the increasing concentration of carbon dioxide in the air resulting from the burning of fossil fuels (coal and oil) is creating a " greenhouse effect" —conserving heat reflected from the earth and raising the world’ s average temperature. If this view is correct and the world’ s temperature is raised only a few degrees, much of the polar ice cap will melt and cities such as New York, Boston, Miami, and New Orleans will be in water.
   Another view, less widely held, is that increasing particular matter in the atmosphere is blocking sunlight and lowering the earth’ s temperature-—a result that would be equally disastrous. A drop of just a few degrees could create something close to a new ice age, and would make agriculture difficult or impossible in many of our top farming areas. Today we do not know for sure that either of these conditions will happen (though one recent government report drafted by experts in the field concluded that the greenhouse effect is very possible). Perhaps, if we are lucky enough, the two tendencies will offset each other and the world’ s temperature will stay about the same as it is now.
This passage is primarily about______.
选项 A、the greenhouse effect
B、the burning of fossil fuels
C、the potential effect of air pollution
D、the likelihood of a new ice age
答案C
解析 主旨题。第一段的前三句提出空气污染的全球性，后三句提出空气污染可能带来的一种后果。第二段前两句指出空气污染可能带来的第二种结果，后两句指出这两种结果发生的不确定性及对将来的美好愿望。由此可知，文章主要论述了空气污染的普遍性及其影响，选项C(空气污染的潜在影响)正确。选项A(温室效应)和选项D(新冰河时代的可能性)只是两种可能性结果。选项B(化石燃料的燃烧)是引起温室效应的原因。故本题选C。
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