Study:
一般时：1、现在 study 2、过去 studied 3、将来 will study 4、过去将来 would study
进行时：1、现在 studing 2、过去 was/were studing 3、将来 will be studing 4、过去将来 would be studing
完成时：1、现在 have studied 2、过去 had studied 3、将来 will have studied 4、过去将来 would have studied
完成进行时：1、现在 have been studying 2、过去 had been studying 3、将来 will have been studying 4、过去将来 would have been studying