[填空题]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 (47) quite seriously by many nations, especially since scientists have warned that the human race will (48) its fresh water supply faster than it runs out of food.
Glaciers are a possible (49) of fresh water that has been overlooked until recently. Threequarters of the Earth’s fresh water supply is still tied up in glacial ice, a reservoir of (50) fresh water so immense that it could (51) 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 (52) over the shallow continental shelf give birth to icebergs