mary could not have received my letter,otherwise she would have replied to me last week.为什么要用would have replied 是过去将来完成时吗?为什么?

could not have done 谁知道could not have must not have been;could not have Do I have to _(clearn) my room?Mary _ (make) her bed every day?Could yuo please __(not go) to the Could not help but have to mary could not have received my letter,otherwise she would have replied to me last week.为什么要用would have replied 是过去将来完成时吗?为什么? Did mary come to the party I do not know .she_wh-Did Mary come to the party I do not know .she_while I was out.-I do not know .She _while I was out.A.may have come B must have come C might come D could come为什么不用D Do you have mary friends?No,I am not.改错 MARY DOES NOT HAVE ANY BOOKS (变肯定句） Mary does not have any books怎样改为肯定句? Mary is ill today.If she _____,she _____ absent from school.A.were not ill,wouldn't beB.had been ill,wouldn't have beenC.had been ill,should have beenD.hadn't been ill,could be can not have visited could have visited must have visited should not have visitedcan not have visitedcould have visitedmust have visited should not have visited could you tell Mary (not talk) on the phone for long考点 He told Mary that he could not go school tomorrow.请问,为什么could用的是过去式? when did your mother_(leave) for dalian?Do I have to _(clearn) my room?Mary _ (make) her bed every day?Could yuo please __(not go) to the movies? In fact,you did not know they could have been could not could not