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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

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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.
It can be concluded that______.
选项 A、raising the world’ s temperature only a few degrees would not do much harm to life on earth
B、lowering the world’ s temperature merely a few degrees would lead many major farming areas to disaster
C、almost no temperature variations have occurred over the past decade
D、the world’ s temperature will remain constant in the years to come
答案B
解析 推理题。根据文章第一段最后一句可知，全球温度只增加几度就会引起极地的大部分冰帽融化，导致有些城市被淹没，选项A(温度只增加几度不会对地球上的生命产生危害)错误。根据第二段第二句可知，全球温度只下降几度就可能带来一个新的冰河时代，许多高海拔区域的农业生产将很难或无法开展，选项B(温度只下降几度会给许多主要农业区域带来灾难)正确。选项C(在过去十年里气温几乎没有变化)文中未提及。根据第二段最后一句可知，如果我们足够幸运，也许这两种趋势将相互抵消，全球温度不变。这只是一种猜测的情况，故选项D(未来几年全球温度将保持不变)错误。故本题选B。
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