By the time Jack returned home from England, his son from college.
A. graduated
B. has graduated
C. had been
D. had graduated
网友回答
A. graduated
B. has graduated
C. had been
(答案→)D. had graduated
解析：考察时态。根据by the time可知，该处要用完成时，因为by是完成时的标志，后面用什么时态就用什么完成时，所以，根据return可知，该处是用过去完成时