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  3. One way of preventing floods may be by making rain ! This may sound rather strange. As we know, heavy rain is the cause of flood

One way of preventing floods may be by making rain ! This may sound rather strange. As we know, heavy rain is the cause of flood

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问题     One way of preventing floods may be by making rain ! This may sound rather strange. As we know, heavy rain is the cause of floods, and in Malaysia most of the floods are caused by the annual monsoon (季风), which brings heavy rain to the east coast. If, however, the rain could be made to fall in the China Sea, there would be no more floods since the rain clouds would not reach the east coast.
    Is it possible to make clouds give up their rain.? Yes, it is, and in 1973 the National Institute of Scientific and Industrial Research (NISIR) suggested that it would be tried. The institute knew of course that it is not possible to make all clouds give up all their rain. It calculated, however, that if the frequency of rainfall could be reduced by 10%, a/id the amount of rain that fell each time could be reduced by 15%, the total amount of flood damage would be reduced by 40%—50%.
    As you probably know, clouds are caused by air containing water-vapor. The air rises and, since water-vapor becomes water when it cools, very tiny drops of water are formed. Since these drops are, very small, they float in the air, and form a cloud. When the cloud rises, however, the drops become colder. Because of this, they join together and become big drops. The big drops are no longer able to float be cause of their size, and they fall. As they fall, they pick up more drops and become bigger. This is the cause of rain.
The third paragraph is concerned with ______.
选项 A、how clouds rise in the air
B、how rain is formed
C、why water-vapor can float in the air
D、how clouds cause rain
答案B
解析 要找出该题的答案关键在于分析第三段的篇章结构。不同于常见的段落，该段的主题句This is the cause of rain位于段末。抓住了这句话就明白了该段的中心内容。
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