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 throughout the year. Icebergs are not like sea ice, which is formed when the sea itself freezes, rather, they are formed (53) 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 (54) to the wind, pulled by subsuce 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 (55) 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 prion of rapid melting in warmer climates and the funneling (传送) 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 (脱盐), or (56) salt from water.

• A) removing
• B) stretch
• C) deriving
• D) entirely
• E) untapped
• F) resource
• G) outgrow
• H) opposite
• I) approximately
• J) considered
  K) similar
  L) source
  M) ensured
  N) sustain
  O) steer