don't u think it is time u ____smoking

问题描述:

don't u think it is time u ____smoking
我知道这是虚拟语句.为什么不是填(should)give up .而是填过去式gave up

it' s time sb did sth.
虚拟语气,并且在这个固定的搭配中,只能用一般过去时.