—Why does the river smell terrible? —Because large quantities of water．A. have pollutedB.

问题补充：

—Why does the river smell terrible?

—Because large quantities of water．

A. have polluted

B. is being polluted

C. has been polluted

D. have been polluted

答案：

A. have polluted

B. is being polluted

C. has been polluted

(答案→)D. have been polluted

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