It took me a long time before I was able to fully appreciate what they __ for me.
问题描述：
It took me a long time before I was able to fully appreciate what they __ for me.
A.had done
B.did
C.would do
D.were doing
寻详解
答
A
此动作发生在was able to之前,即表示发生在过去的过去,用过去完成时