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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 considered quite seriously by many nations, especially since scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food.
    Glaciers are a possible source 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 untapped fresh water so immense that it could sustain 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 stretch 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 entirely 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 opposite 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 corral them and steer them to parts of the world where they are needed would not be too difficult.
    The difficulty arises in other technical matters, such as the prevention of rapid melting in warmer climates and the funneling of fresh water to shore in great volume. But 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, or removing salt from water.
What is the main topic of the passage?
选项 A、The movement of glaciers.
B、Icebergs as a source of fresh water.
C、Future water shortages.
D、The future of the world’s rivers.
答案B
解析 主旨题。文章以一个看似为joke的方法：把冰山拖到世界上人口稠密的地区和干旱地带，再从中获取淡水，作为开头，引出人类将在耗尽粮食之前首先耗尽淡水资源的问题。接着在文章的第二段首句点题，glaciers直到最近以前一直被忽视可能的source of fresh water，后两段分别介绍了冰山的冰和从冰山取淡水的技术问题。原文第二段首句中的Glaciers与选项B中的Icebergs对应，asource of flesh water与选项B重现。故答案为B。
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