Question

I don t think he could have done so much homework last night

Answer 1

情态动词+have 过去分词 都表示对过去的事实进行推测,与表示过去时间的状语连用时,相当于一般过去时.如：You must have stayed very late last night,didn't you?

但是,不与过去时间连用时,则指过去的动作对现在产生影响,相当于现在完成时.如：

You must have seen the film Titannic,haven't you?你肯定看过电影泰坦尼克了,不是吗?(那我就不邀你去看了）