2. 外语
  3. One day, drought(干旱)may be a thing of the past at least in coastal cities. Vast areas of desert throughout the world may for the

One day, drought(干旱)may be a thing of the past at least in coastal cities. Vast areas of desert throughout the world may for the

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问题     One day, drought(干旱)may be a thing of the past at least in coastal cities. Vast areas of desert throughout the world may for the first time【C1】______to life and provide millions of acres of【C2】______where now nothing grows.
    By the end of this century this may not be mere【C3】______. Scientists are already looking for the【C4】______of using some of the available ice in the polar regions. In these regions there are vast ice-caps formed by snow【C5】______over the past 50,000 years. Layer【C6】______.layer of deep snow means that, when melted,  the snow water would be pure, not salty【C7】______sea-ice would be. There is so much potential pure water here【C8】______it would need only a fraction of it to turn much of the desert or poorly irrigated parts of the world【C9】______rich farmland. And what useful packages it would come in! It should be【C10】______to cut off a hit of ice and transport it!
    【C11】______perhaps a passing iceberg(流冰)could be captured. They are always breaking away from the main caps【C12】______around, pushed by currents, until they eventually melt and are wasted. Many icebergs are, of course, far too【C13】______to be towed any distance, and would melt before they reached a country that needed them anywhere. It would be necessary to【C14】______one that was manageable and that was big enough to provide a good supply of ice when it【C15】______us. Engineers think that an iceberg up to seven miles long and one and a half miles wide could be transported【C16】______the tug pulling it was as big as a supertanker] Even then they would【C17】______only twenty miles every day. However, once the iceberg was at its【C18】______, more than 7,000 million cubic meters of water could be【C19】______from it!
    That would probably be more than enough for any medium-sized city【C20】______in the hottest summer! But no doubt use could be made for it.
【C6】
选项 A、on
B、upon
C、after
D、over
答案B
解析 upon在此帮助构成习惯表达方式，layer upon layer意思是“一层又一层地”。
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