问题
选择题
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
答案
答案：A
考查时态。从句的动作发生在谓语动词之前，题中谓语动词为took，“过去的过去”应用过去完成时态。故选A。
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