单项选择题

According to this passage, two research teams ______.

A．have determined the full range of contaminants in the water supply
B．have ascertained the geographic extent of the water pollution
C．have developed new methods to measure water contaminants
D．have succeeded in preventing drinking water from being polluted
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单项选择题
The second sentence of the first paragraph, We have lived through..., off a hound , intends to say that ______.
A．many rivers and creeks have been excessively polluted by various contaminants
B．our lives depend on flaming rivers and caustic creeks
C．we cannot prevent rivers and creeks from being hounded
D．people cannot live without the supply of water from rivers and creeks
单项选择题
The two research teams mentioned in the passage endeavor
A．to track samples at more sewage-treatment facilities
B．to determine latent chemical dangers in the water
C．to measure the exact amount of any drug found in drinking water
D．to find out the precise number of contaminants in freshwater streams
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