三．主语从句中的虚拟语气
It is+形容词/ 名词/ 过去分词+ that 引导的主语从句,用虚拟语气即从句谓语动词用(should )+动词原形，should 可以省略。
常用形容词：necessary, important, essential, imperative, urgent, preferable, vital, advisable 等 常常用名词：duty, pity, regret, no wonder, shame 等。
常用过去分词：demanded, suggested, required, requested, ordered, decided等Eg: It is suggested that pupils (should) wear school uniforms.
It is important that everyone (should) inform themselves of these rules. It is a pity that he (should) refuse to accept the offer.
 
四．其他形式的虚拟语气

1. It's (high/about) time +that 从句 该句型用虚拟语气 译为“该干某事了” 谓语动词用过去式或者 should+动词原型，其中 should 不能省略。

Eg:It is high time that you went to school.

1. wish 引导的宾语从句和 as if, as though，if only 引导的状语从句，用虚拟语气。

	从句
与现在事实相反	一般过去时
与过去相反	had+done
与将来相反	would/could/should/might + 动词原形

Eg: He felt as if he were responsible for what had happened.
He treats me as if I were a stranger.
Look at the terrible situation I am in! If only I had followed your advice. If only I had not been busy last week.
（3)would (had) rather, would as soon, would sooner 其后的宾语从句用虚拟语气

	从句
对现在/将来	一般过去时
对过去	had+done

Eg: I would rather he went right now.
（4) lest, in case, for fear that 引导的目的状语从句，用虚拟语气即从句谓语动词用(should )+动词原形，should 可以省略。
Eg: The old man walks slowly for fear that he (should) fall down.
 
五．“情态动词+have done”的用法
must have done 过去一定做过某事
can't / couldn't have done 过去不可能做过某事
may have done 过去可能做过某事
might / could have done 过去可能做过某事，或者表示本能够做某事而实际上没做
should / ought to have done 表示本应该做某事而实际上没做
needn't have done 表示本不必做某事而实际上做了
例如：— I left my handbag on the train, but luckily someone gave it to a railway official.
— How unbelievable to get it back! I mean, someone  it.
A. will have stolen B. might have stolen C. should have stolen D. must have stolen