She had just finished her homework her mother asked her to practice playing the piano yesterday.
A. when
B. while
C. after
D. since
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(答案→)A. when
B. while
C. after
D. since
解析： 考查固定结构。had just done sth when…某人刚刚做了某事，这时。。。句意：昨天她刚写完作业她妈妈就让她练习弹钢琴。选A。