关于虚拟语气问题

时态倒退，可参考以下例子
a. 同现在事实相反的假设。
句型 ： 条件从句 主句
一般过去时 should/would/could/might+动词原形
If they were here, they would help you.
b. 表示于过去事实相反的假设。
句型： 条件从句 主句
过去完成时 should/would/could/might have+ 过去分词
If she had worked harder, she would have succeeded.
The rice would not have been burnt if you had been more careful.
If my lawyer had been here last Saturday, he would have prevented me from going.
If he had come yesterday, I should / would have told him about it.
含义：He did not come yesterday, so I did not tell him about it.
If he had not been ill and missed many classes, he would have made greater progress.
含义： He was ill and missed many lessons, so he did not make greater progress.
c. 表示对将来的假想
句型： 条件从句 主句
一般过去时/were+ 不定式/should+ 动词原形 should/would/could/might+ 动词原形
If you succeeded, everything would be all right.
If you should succeed, everything would be all r