问题
选择题
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
答案：D
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。