was doing 与did 之间的区别.

was、were与did用法的区别 do did does doing 的区别 do 和 to do ,doing ,to doing 他们之间的区别与联系.很晕啊 it was hard to do与it was hard doing的区别 have been doing 和was doing的区别 doing与 todo的区别 go on to do sth.与go on doing sth.之间的区别到底在什么地方? do,did与is,was提问j时的区别是什么? 过去式的be动词+动词的什么形式?doing或者did?如was doing my housework,was trap was/were后接doing还是did 请问stop doing与stop from doing的区别 be always doing与have always been doing的区别