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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
【C7】
选项
答案D
解析 本句的结构完整。因此需要副词成分。空格前的插入成分rather表明冰山的形成与海上浮冰不同，海上浮冰是海水自身冻结形成．而冰山是在陆地上形成。词库中只有entirely“完全”能突出二者不同的程度。副词ap-proximately常用于形容大概的数字、数量或时间，不宜用在此处。
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