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
Which of the following statements is true
A．Altogether 95 different contaminants have been found in streams.
B．Nearly 80 percent of the streams surveyed contains only the familiar contaminants.
C．The most frequently detected contaminants are usually in low concentrations.
D．The average number of contaminants in each stream surveyed is seven.
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
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