it is high time that we ( ) to think how to deal with the problem of air pollution.A.began B.would begin C.begin.D.should begin.如何选,为什么?

it is high time that we ( ) to think how to deal with the problem of air pollution.A.began B.would begin C.begin.D.should begin.如何选,为什么?
it is high time that we ( ) to think how to deal with the problem of air pollution.
A.began B.would begin C.begin.D.should begin.如何选,为什么?

it is high time that we ( ) to think how to deal with the problem of air pollution.A.began B.would begin C.begin.D.should begin.如何选,为什么?
A,固定结构,It's time sb did sth.

D 现在该是我们要考虑如何处理空气污染问题的时候了
it is high time that 。。。should+动/原

A或者D
是虚拟，It's (high) time +should do/did sth
从句谓语动词要用过去式或用should加动词原形，但should不可省略