－Why does the river smell terrible?－Because large quantities of waterA. have been pollut

问题补充：

－Why does the river smell terrible?

－Because large quantities of water．

A. have been polluted

B. is being polluted

C. has been polluted

D. have polluted

答案：

(答案→)A. have been polluted

B. is being polluted

C. has been polluted

D. have polluted

解析：考查时态。根据语境可知，大量的水已经被污染，故用现在完成时态的被动语态。句意：——为什么这条河这么难闻？——因为大量的水已经被污染。故A正确。