关键要理解Was在句中所起到的时态功用。copysince he graduated form Yale. 自从从耶鲁大学毕业zhidaosince he was a student at Yale.自从他不是耶鲁的学生了（有可能是毕业，有可能是肄业...）Since I was ill 不再生病（病好了）=since I recovered 病愈 举个例子 She was beautiful.

1.他从耶鲁大学百毕业后已经有过几个工作。2.自从他不在是耶鲁学习以来，他已经有度过几个工作了。since作为连词“自。。。以来”问讲时，引导的从句谓语既可答以是延续性的，也可以是瞬时性的。回但都表示是动作的完成，故谓语是延续性动词时，表答示“不在那个动作状态”。it's two weeks since i was ill=it's two weeks since i recovered.