Mary had finished her homework__the time I got home.

Mary had finished her homework__the time I got home.
A、until
B、at
C、by
D、when
【正确答案】：C
【题目解析】：by the time+从句，是过去完成时态常用的时间状语。这时，主句用过去完成时，从句用一般过去时。译为：当……时候，……已经……。我到家时，玛丽已经做完作业了。