英语高手请讲

虚拟语气
1.表示与现在事实相反的假设，状语从句的动词用一般过去时（BE用were），主句动词用助动词should，would，could，might＋原形动词。
If I were you, I would help her.
如果我是你，我会帮助她。
2.表示与过去事实相反的假设或想象，状语从句的动词用过去完成时，主句动词用助动词＋HAVE＋过去分词。
If I had visited the place before, I would have known the way.
如果我去过那个地方，我就认识路了。
3.表示与将来事实相反的假设，状语从句的动词用were＋to＋原形动词或should＋原形动词，主句用助动词should，could，would，might＋原形动词。
If it were to snow in the summer, I would believe you.
倘若夏天下雪，我才会相信你。
4.表示现在或将来可能发生的事情，状语从句的动词用一般现在时，主句的动词用助动词加原形动词。
If it stops raining tomorrow, we will go out.
如果明天不下雨，我们就出去。
5.在这类条件句中，各种现在时都可用在if引导的从句中，而不仅仅是一般现在时。
If Sara is talking to him, she will know everything.
如果莎拉现在正同他谈话，她就会知道一切。
If she has found it, she will come back soon.
如果她已经找到了，她很快就会回来。
If he has been driving all night, he will need a good sleep.
若他整夜都在开车，他就需要好好睡一觉。

引起虚拟语气的词
1.在wish后的从句用过去时表示与现在事实相反的假设；用过去完成时表示与过