如果從句和主句都表示過去的,那從句用had done,主句用would ,could,might,should+have done
如：If you had taken my advice,you would not have been late for the meeting yesterday.如果從句表示過去的,但主句表示現(xiàn)在的,從句用had done,主句用would ,could,might,should+do,如：If you had taken my advice,you would not be late for the meeting now.這種一般都有個(gè)時(shí)間,如果沒有表示時(shí)間的詞也可以從上下文看出.