By the time he was fourteen,he___what he wanted to be when he ___up.

问题描述:

By the time he was fourteen,he___what he wanted to be when he ___up.
A.knew,grows B.knew,grew C.had known,grew D.has known,grows
选什么,为什么.

选B
有具体时间不能用完成时态 所以只能选knew
后面的时态要跟前面一致 所以要用一般过去时 选择grew