题目内容：

根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。 

Obtaining Fresh Water from Icebergs

  The idea of getting fresh water from icebergs that are moved to populated areas or places was once treated as a joke. Recently, scientists have warned that the human race will outgrow its fresh water supply faster than it runs out of food.___ 1.___

Glaciers are a possible source of fresh water that has been overlooked until recently. __2.__It contains fresh water so much that it could sustain(维持) all the rivers of the world for 1,000 years. Huge glaciers that stretch over the shallow continental shelf give birth to icebergs throughout the year.__ 3.__ However, 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. 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(赤道) in the Atlantic Ocean. __4.__ The difficulty exists such as its rapid melting in warmer climates. __5.__

A. Icebergs are not like sea ice, which is formed when the sea itself freezes.

B. Now it is being considered quite serious by many nations.

C. 7,659 trillion metric tons of ice are floating on the sea every year.

D. But the water they could provide would be far cheaper than that produced.

E. To move them to dry parts of the world would not be too difficult.

F. It is not a dream to get water from icebergs.

G. Three-quarters of the Earth’s fresh water supply is still tied up in glacial ice.