--- 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
网友回答
A. have polluted
B. is being polluted
C. has been polluted
(答案→)D. have been polluted
解析：表示动作发生在过去，但一直持续到现在，并且有可能继续持续下去，故用现在完成时，又因为主语“water”与动作“pollute”之间是被动关系，故用被动语态，所以这里需要用现在完成时的被动语态。