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  3. The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once trea

The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once trea

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问题     The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real life. But now it is being【C1】______quite seriously by many nations, especially since scientists have warned that the human race will【C2】______its fresh water supply faster than it runs out of food.
    Glaciers are a possible【C3】______of fresh water that has been overlooked until recently. Three-quarters of the Earth’s fresh water supply is still tied up in glacial ice, a reservoir of【C4】______fresh water so immense that it could【C5】______all the rivers of the world for 1,000 years. Floating on the oceans every year are 7,659 trillion metric tons of ice encased in 10,000 icebergs that break away from the polar ice caps, more than ninety percent of them from Antarctica.
    Huge glaciers that【C6】______over the shallow continental shelf give birth to icebergs throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes, rather, they are formed【C7】______on land, breaking off when glaciers spread over the sea. As they drift away from the polar region, icebergs sometimes move mysteriously in a direction【C8】______to the wind, pulled by subsurface currents. Because they melt more slowly than smaller pieces of ice, icebergs have been known to drift as far north as 35 degrees south of the equator in the Atlantic Ocean. To control them and【C9】______them to parts of the world where they are needed would not be too difficult. Even if the icebergs lost half of their volume in towing, the water they could provide would be far cheaper than that produced by desalinization(脱盐), or【C10】______salt from water.
A)removing I)approximately
B)stretch J)considered
C)deriving K)similar
D)entirely L)source
E)untapped M)ensured
F)resource N)sustain
G)outgrow O)steer
H)opposite
【C3】
选项
答案L
解析 空格前面的冠词a表示此处需要可数名词单数形式，且与of一起连用。后一句讲到，地球上3／4的淡水埋藏在冰川之中。可见，Glaciers(冰川)是淡水的一个来源，source“来源”符合语境。
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