They had finished all the work _ yesterday morning选择题, 求答案和解释 A. atB.byC.toD.on
问题描述：
They had finished all the work _ yesterday morning
选择题, 求答案和解释
A. at
B.by
C.to
D.on
答
注意这儿用了had finished说明是过去完成时.该句意思是到昨天早上为止他们完成了所有的工作,“到.为止”用by.
by+过去的某一时间点,用过去完成时；by+将来的某一时间点,用将来完成时