—Why does the lake smell terrible? —Because large quantities of water .A. have polluted.B.

问题补充：

—Why does the lake 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.

解析：从问句和答语可知说的是湖的现在的情况，又因为强调污染对湖所产生了一定的结果和影响，故在C，D中选择正确答案。由于主语是quantities，谓语动词要用复数。故选D。