一道英语选择(初三)

问题描述:

一道英语选择(初三)
Peter asked Tom whether the teacher _______ 5 minutes _______.
A.has been there;before
B.had been there;ago
C.had been there;before
为什么?

C
用现在完成时,但有asked就要用过去完成时;ago只能用过去时