现在完成时since的用法

1、since+过去一个时间点 (如具召搁体的年、月、日侮信期、钟点、 1980, last month, half past six)。

I have been here since 1989.

2、since +一段时蚊沫虚间+ 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.