It is high time that we ____ measures to bring water pollution under control

C

It's high time...后面要接虚拟语态，一般用一般过去式，也可以加should+V原

C
这是个虚拟语气句：it is (high) time that+sb. (should) do...
It is high time that we __take__ measures to bring water pollution under control.也对
high表程度，强调事情必须该办了

C
It's time that后加should+动词原形
表示虚拟语气

c

我们是时候该采取些方法来控制水污染了。

C