America is in no immediate danger of "running out of water". People in the West have been aware that water is a precious commodi

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问题     America is in no immediate danger of "running out of water". People in the West have been aware that water is a precious commodity and must be conserved. In the damp East, an excess of water led to complacency until two factors created concern over our water supply. First, the periods of drought from 1961 to 1966 in the Northeast affected crop production and used up the surface and ground water supplies. Second, attention was called to rapid increases in the rates of pollution of these waters resulting from increased urban and industrial growth. As a result, there is an increasing awareness of the need for conserving the quantity and quality of our nation’s water supplies.
    Water is a renewable resource, but it is not exhaustible. When used for municipal, industrial, or agricultural purposes, it is not destroyed, but generally finds its way back into our water supply. This used water now carries some waste materials. These dirty waters are often dumped into large bodies of water or are disposed of on land. In the latter instance, evaporation concentrates some of the wastes on the soil surface. On the other hand, water moving through the soil will eventually carry some of the wastes down into the ground water supplies. Eventually, all water evaporates and later returns to the earth as rain or snow in a relatively purer state.
    Through this never-ending cycle, there is just as much water in this country now as there ever was. The amount, however, does not increase. Our rapid population growth and our agricultural and industrial expansion have caused our water needs to soar. By withdrawing water from streams too quickly, we have in some instances upset the balance of nature’s built-in renewal processes for conserving water. As a result, some of our streams and lakes have become "wet deserts. " There is still plenty of water in them, but its water is so polluted that it supports almost no life at all.
The passage is mainly about________.

选项 A、water resources of the United States
B、the renewal processes of water in nature
C、the importance of water conservation
D、water pollution in America

答案C

解析 主旨题。文章第一段的最后一句“As a result,there is an increasing awareness of the need for conserving the quantity and quality of our nation’s water supplies.”是文章的中心思想,指出人们越来越意识到保护水的量和质的必要性。第二、第三段主要讨论节约用水和水污染的危害。第二段指出,水虽然是一种可再生的资源,但并不是用之不竭;第三段说,人口的急剧增加,工农业的快速发展使得用水需求高涨并造成严重的水污染。综上所述,我们可以看出,文章主要讨论保护水资源的重要性。A选项“美国的水资源”,B选项“自然界水资源的更新进程”,D选项“美国的水污染”都是以偏概全。
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