虚拟语气if的三种用法
问题描述：
虚拟语气if的三种用法
答
三种情况,(1)对过去,从句had done主句would/could/might/have done(2)对现在,从句：did /were主句：would/could/might do(3)对将来,should do/were to do/did.从句,更上一个一样.注意,“主将从现”原则.