since作为介词后边接某一确定的时间点，主句谓语动词是持续性动词，常与现在完成时态、现在完成进行时态或过去完成时态连用。ever since后面可以不加任何东西，也可以加名词或者加从句。
since的用法1.since+过去一个时间点（如具体的年、月、日期、钟点、1980， last month， half past six）。
I have been here since 1989.
2.since+一段时间+ago
I have been here since five months ago.
3.since+从句
Great changes have taken place since you left.
Considerable time has elapsed since we have been here.
4.It is+一段时间+since从句
It is two years since I became a postgraduate student.
5.用于句型“一段时间+has passed since+时间状语从句”中，译作“自从…以来， …（时间）已经过去了”。
