I don't know _______________.A.why do this B.why having done this C.why doing this

问题描述:

I don't know _______________.A.why do this B.why having done this C.why doing this
D.why we ought to do this
请问,选什么,为什么呢?

选D,因为其他三项没主语,
你好聪明哦,不贴出答案,防止某些人浑水摸鱼,因为这里是一个宾语从句,在从句中,除了where to do,what to do,how to do这三个结构外,其他的都必须要有主谓宾结构,你的A B C项,均却主语,所以,你明白为什么了吧