by the time后面加什么时态的

　　You count such a watch by the time he starts his class.

　　你总是掐着他开始上课的时间。

　　Most of the workers had already rung in by the time I arrived.

　　我到的时候，大多数工人都已签到了。

　　By the time she left college, she had been an excellent student.

　　到她大学毕业的时候，她已经是一个优秀的学生了。