I can't remember ___i sent the book to A that B when C where D whom请说明一下为什么

I can't remember ___i sent the book to A that B when C where D whom请说明一下为什么
I can't remember ___i sent the book to A that B when C where D whom
请说明一下为什么

I can't remember ___i sent the book to A that B when C where D whom请说明一下为什么
whom,这里用了sent to,空里填的应是对sent to的宾语的疑问词,所以用whom.

D
send sth to sb（宾格）

C

C 意思是我记不得我把书送到哪去了 关键是to 如果没to的话B C都行

D
I sent the book to是定语从句， 从句中缺少介词to的宾语，即把书寄给的人， 因此排除A, B, C