I was told that the book _____to the library on time. a must return b must be return

问题描述:

I was told that the book _____to the library on time. a must return b must be return
c must be returning 为什么选b不而不能选a,谢谢有知识的朋友!fast!1

书是被归还,所以要用被动式,所以要选B