We wanted to tell them_______these books.A.when return B,when to return C when return D when you return 选择哪一个?为什么

问题描述:

We wanted to tell them_______these books.A.when return B,when to return C when return D when you return 选择哪一个?为什么

B,when to return
疑问副词+动词不定式to do
等同于一个完整的句子
比如此句
,when to return these books=when they should return these books.