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

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

(答案→)C. has been polluted

D. have been polluted

解析：考查时态，因为主语large quantities of water和动词pollute是动宾关系，所以用被动语态，由前面的问子，可以知道水已经被污染，因为主语large quantities of water是单数，所以选C