单项选择题

What percentage of the earth's water can man actually use at present

A．Nearly 75 per cent.
B．About 97 per cent.
C．Exactly 3 percent.
D．Less than 3 per cent.
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单项选择题
The phrase the world in the first line of the passage refers to
A．"man".
B．"you".
C．"woman".
D．"they".
单项选择题
According to the passage, sea-water can be turned into fresh water by
A．heating it up.
B．treating it with chemicals.
C．taking salt out of it.
D．drying it up.
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