问题
选择题
--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
答案
Ｄ
考察主谓一致。large quantities of 放在句首，谓语动词永远都使用复数形式，根据句意可知是被动一意思，故D正确。