（误）I shouldn't do that if I was you.
（正）I shouldn't do that if I were you.（表示与现在事实相反的虚拟语气不能用was，只能用were.）
（误）If my father were here now，he will tell me what to do.
（正）If my father were here now，he would tell me what to do.（表示与现在事实相反的虚拟语气中，主句的助动词只能用would，might等过去时。）
（误）If I knew her telephone number，I would have called her.
（正）If I had known her telephone number，I would have called her.（表示与过去事实相反的虚拟语气中，条件从句的动词要用过去完成时。）
（误）If it had not rained yesterday，he might come.
（正）If it had not rained yesterday，he might have come.（表示与过去事实相反的虚拟语气中，主句的动词要用助动词的过去时might，could等+HAVE+过去分词。）
（误）I don't think that I shall fail. But if I failed，I would try again.
（正）I don't think that I shall fail. But if I should fail，I would try again.（表示与将来事实相反的虚拟语气中，条件从句的动词用should加原形动词。）
（误）Did he bring some money with him，he would have bought it.
（正）Had he brought some money with him，he would have bought it.（表示与过去事实相反的虚拟语气中，条件从句的动词要用过去完成时，若省略if，则用倒装形式。）
（误）Be she a man，she might be elected president.
（正）Were she a man，she might be elected president.（表示与现在事实相反的虚拟语气，不能用was，只能用were;若省略if，则将were放在句首。）
（误）I suggested that the teachers' wages could be increased.
（正）I suggested that the teachers' wages should be increased.（suggest当建议讲时，后面的名词从句的主要动词要用should加原形动词，should可以省略。）
（误）It is important that he will do it.
（正）It is important that he do it.（It is important+that引导的名词从句的动词要用should加原形动词，should可以省略。）