By the time Jack returned home from England，his son from college.(2011·辽宁)
A. graduated
B. has graduated
C. had been graduating
D. had graduated
网友回答
A. graduated
B. has graduated
C. had been graduating
(答案→)D. had graduated
解析：考查时态。句意：杰克从英格兰回到家时，他的儿子已经大学毕业了。by the time...“到……的时候”引导时间状语从句时，如果从句的谓语动词用一般过去时，主句的谓语动词要用过去完成时。