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.
Water is relatively purer in________.

选项 A、fast moving streams and rivers
B、underground water supplies
C、mountainous areas
D、rain and snow

答案D

解析 细节题。根据文章第二段最后一句“Eventually, all water evaporates and later returns to the earth as rain or snow in a relatively purer state. ”可知最终所有的水蒸发,然后以降雨或降雪等相对较纯净的形式回到地球,故选D。
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