单选题：第50题____________

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题目类型：单选题
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题目内容：

第50题____________ A．A limited water supply.
B．so that it can be used again just as if it were fresh from a spring.
C．It is possible to purify large amounts of sea water.
D．But even if every large city purified and reused its water.
E．And we cannot even use all of that.
F．Experiments have already been done in this field.

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答案解析：

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分类：综合类题型：单选题

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分类：综合类题型：单选题

The writer introduces each category in the passage by______

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The increase of greenhouse gases __________.

The increase of greenhouse gases __________.A．will influence future climate chan

分类：综合类题型：单选题

Paragraph 5__________

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分类：综合类题型：单选题