The world is not only hungry, but thirsty for water. That may seem【B1】______to you, since nearly 75% of the earth’s surface is【B

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问题     The world is not only hungry, but thirsty for water. That may seem【B1】______to you, since nearly 75% of the earth’s surface is【B2】______with water, but about 97% of this【B3】______amount is sea water, or salt water. Man can only drink and use the other 3%—the fresh water from rivers, lakes, underground, and other【B4】______. And we cannot even use all of that, because some of it is in the form of【B5】______and glaciers. Even worse, some of it has been【B6】______.
    However, this small amount of fresh water is still enough for us, but our need for water is increasing【B7】______. Only if we take steps to deal with the problem now can we avoid a【B8】______worldwide water shortage later on.【B9】______. Today water is used only once and then discharged into a sewer system, and it eventually returns to the sea or runs into underground storage tanks. It is possible to pipe used water to a purifying plant.【B10】______.
    Even if every large city purified and reused its water, we still would not have enough.【B11】______. If we take these steps, we’ll be in no danger of drying up!
【B10】

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答案There it can be filtered and treated with chemicalsso that it can be used again

解析 filtered,treated with,chemicals,used again
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