单选题 One billion people in the world are short of water. How can this problem be solved? Some suggestions have been to desalinate (除去盐分) ocean water or to build enormous water pipelines from areas where water is abundant. Suggestions such as these prove extremely costly when they are actually used. One possibility that scientists are considering is pulling icebergs from either the North Pole or the South Pole to parts of the world with a water shortage. Although many questions must be answered before such a project could be tried, moving icebergs seems a reasonable possibility in the future.
Engineers, mathematicians, and glaciologists (冰川学家) from a dozen countries have been considering the iceberg as a future source of water. Saudi Arabia is particularly interested in this project because it has a great water shortage. Scientists estimate that it would take 128 days to transport a large iceberg (about 1/2 miles square) to Saudi Arabia. Yet the iceberg would be completely melted by the 104 ^th day. Therefore, insulation would be essential, but how to insulate the iceberg remains an unsolved problem.
The problems in transporting an iceberg are numerous. The first problem is choosing the iceberg to pull. The icebergs that form in the North Pole are quite difficult to handle because of their shape. Only a small portion extends above the water—most of the iceberg is below the surface, which would make it difficult to pull. South Pole icebergs, on the other hand, are flat and float like table tops; thus, they would be much easier, to move.
How can a 200 million-ton iceberg be moved? No ship is strong enough to pull such enormous weight through the water. Perhaps several ships could be used. Attaching ropes to an iceberg this size is also an enormous problem. Engineers think that large nails or long metal rods could be driven into the ice. What would happen if the iceberg split into several pieces during the pulling? Even if an iceberg with very few cracks were chosen, how could it be pulled through stormy waters? Furthermore, once the iceberg reached its destination, very few ports would be deep enough to store it.
All of these problems must be solved before icebergs can become a reasonable source of water. Yet scientists estimate that it will be possible to transport them in the near future. Each year, enough icebergs form to supply the whole world with fresh water for a full year. In addition, icebergs are free and nonpolluting. As a solution to the world"s water problems, icebergs may be a workable possibility.

单选题 Desalinating ocean water might be rejected as a means to provide fresh water in practice in that ______.

单选题 Which of the following is a problem in transporting icebergs?

单选题 Icebergs from the South Pole probably are easier to transport because ______.

单选题 From the passage, the word "insulation" (Para 2, Line 5) can be best explained as ______.

单选题 From the passage we can infer that ______.