since的用法是什么？

since的用法是什么？

since的用法有两点：一表示“自从……以来”，二是表示“既然”之意。

since的四种用法 

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.