题目内容：

We didn"t finish the work in time. You____us since you were there.
A)might help B)should help C)could have helped D)must have helped

优质解答

正确答案应该是C选项.表示本能帮助我们却没有帮助.
英语中,表达与过去事实相反的虚拟可以用情态动词过去式+have done的形式.
如could have done;本能做而没做.might have done本可能做而没做.
should have done 本应该做而没做.must have done本一定要做而没做.
而在情态动词后加not变为否定时,表示本没有...却做了.
如couldn't have done 本不能做而做了.shouldn't have done 本不该做而做了.