问题
选择题
By the time Jack returned home from America, his son __________ from college.
A．graduate
B．has graduated
C．had graduated
D．had been graduated
答案
答案：C
考查时态。By与完成时连用，本题by后面是表示过去的时间，所以使用过去完成时。句意：到JACK回到美国的时候，他儿子已经大学毕业了。