求大神解决虚拟语气的结构于用法前阵子看书了,学习到虚拟语气,可是书本上的太深奥,我是自学的,求大神总结起来简单说明

在第一种情况下，与过去事实相反，主句谓语动词：would have done ，从句谓语：had done ；EX: If he had known it,he would have told me . 与现在事实相反，主句谓语：would do 从句谓语：were、 did（过去式）； EX: what would you do if you were in his place? 表示将来的推测，主句谓语：would do 从句谓语：were to do、should do . EX: If she should encounter any difficulty in her life, her sister would help her out. 第二种， 对过去愿望：从句谓语：had done 、could have done ； EX：I wish i had forgotten it. 对现在或将来愿望：从句谓语：could do 、were EX: I wish i could fly. / I wish i were a bird. 第三种，对过去事实假设：从句谓语：had done； EX:The animal was walking as though it has hurt its leg. 对现在事实假设：从句谓语：were、did（过去式）； EX:She talks as if she were innocent. 对将来事实假设：从句谓语：would do EX: It seems as if the meeting would never end. I HOPE IT CAN HELP YOU.