问题
选择题
By the time Jack returned home from England, his son_____ from college.
A．graduated
B．has graduated
C．had been
D．had graduated
答案
答案：D
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