文档介绍：情态动词的完成时(表示对过去的说法)
must +have +过去分词 （用于肯定句）一定已经…….
The light is still on. They must have forgotten to turn it off when they left the room.
注:mustn’t have done ×
can’t (couldn’t) +have +过去分词 （用于否定或疑问句）不可能……..
He cannot have been to that town for I saw him just now.
should/ought to +have+过去分词 本应该做(却没有做)…….
As his best friend, you should/ought to have helped him. (but in fact, you didn’t.)
shouldn’t /ought not to +have +过去分词 本不应该做(却做了)…….
You shouldn’t have parked your car here, for it’s a public place.
needn’t +have +过去分词
本不必做……
You needn’t have waited for me. I told you yesterday I would overwork.
with
with + done
With the homework finished, the boy went out.
with + doing
With the old man leading the way, we finally find the house.
with + prep
With the light on, all the students went out of the classroom.
虚拟语气的用法
概念：表示说话人的愿望、假设、猜测、或建议，而不表示客观存在的事实。虚拟语气通过谓语动词的特殊形式来表示
虚拟语气用于条件状语从句
(1) 与过去事实相反
If…had +done, …would (should, could, might) +have +done
If you had taken my advice, you wouldn’t have failed in the exam.
与现在事实相反
If + did (be→were)，…would (should, could, might) + do
If he had time, he would attend the meeting.
If I were you, I should study English.