Did you know _____ at the bus stop?

题目

Did you know _____ at the bus stop?
maybe their teacher.
a.who are they waiting for b.whom they are waiting for
c.whom they were waiting for
这个题选择哪一个呢?我知道这个题应该是陈述句.但是我不知道为什么会选择C而不是A?..

答案

选 C.
由于宾语从句要用陈述句词序,故不能选 A.
又因为主句为过去时,故宾语从句也要用过去时,故不能选 B