为什么最后用had fallen 过去完成时,而不用过去式?When I CAME back into the house,it was raining (去more）harder and harder.Then I heard a loud crashing sound from (去the）back of the house.When I ran out to find out WHAT had happen

为什么最后用had fallen 过去完成时,而不用过去式?When I CAME back into the house,it was raining (去more）harder and harder.Then I heard a loud crashing sound from (去the）back of the house.When I ran out to find out WHAT had happen
为什么最后用had fallen 过去完成时,而不用过去式?
When I CAME back into the house,it was raining (去more）harder and harder.Then I heard a loud crashing sound from (去the）back of the house.When I ran out to find out WHAT had happened,a big tree had fallen down and BROKEN the top of the backroom.

为什么最后用had fallen 过去完成时,而不用过去式?When I CAME back into the house,it was raining (去more）harder and harder.Then I heard a loud crashing sound from (去the）back of the house.When I ran out to find out WHAT had happen
ran已经是过去式了,倒了发生在ran的前面,过去的过去用had done

因为最后表过去已经完成过了，用我们老师教的话说：老祖宗传下来的，只要记住就行。