问题

(2013·陕西师大附中模拟)If we had taken such effective measures much earlier, the river ________ so seriously now.
A:is not polluted
B:would not be polluted
C:had not been polluted
D:would not have been polluted
B:would not be polluted
C:had not been polluted
D:would not have been polluted
正确答案是: