问题
选择题
By the time they arrived at the station, the train .
A．will leave
B．would leave
C．has left
D．had left
答案
答案：D
题目分析：句意：到他们到达火车站是，火车已经离开了。根据By the time they arrived at the station,可知到达这个动作发生在过去，火车离开是在他们到达之前，故用过去完成时。故选D。