单项选择题

What percentage of the total earth's water does underground water make up

A．0.05%.
B．0.5%.
C．4.5%.
D．5%.
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单项选择题
Clouds are formed from ______.
A．evaporation
B．water vapor
C．outer space
D．the hydrologic cycle
单项选择题
The supply of ground water is getting low because of ______.
A．conservation
B．poisonous water
C．pollution
D．population increase
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