—Whydoestheriversmellterrible?      —Becauselargequanti...

问题详情：

—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

【回答】

D

知识点：动词时态与语态

题型：选择题