It is well known to us all that a lot of rivers by factories.A. are pollutingB. have been

问题补充：

It is well known to us all that a lot of rivers by factories.

A. are polluting

B. have been polluting

C. are being polluting

D. are being polluted

答案：

A. are polluting

B. have been polluting

C. are being polluting

(答案→)D. are being polluted

解析：考查时态语态，river和pollute是被动关系，但四个选项只有D项是现在进行时的被动，句意是：众所周知的是很多河流正在被工厂污染。选D。