单项选择题

The best title for this passage is ______.

A．Water Conservation
B．The Hydrologic Cycle
C．Underground Water
D．Polluted Groundwater
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单项选择题
Clouds are formed from ______.
A．water vapor
B．evaporation
C．the hydrologic cycle
D．groundwater
单项选择题
The supply of groundwater is getting low because of ______.
A．conservation
B．toxic waste
C．pollution
D．population increase
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