1) since 以往一个时间点 (如实际的年、月、日期、钟点、1980, last month, half past six)。I have been here since 1989.2) since 一段时间 agoI have been here since five months ago.3) since 从句 Great changes h
1) since 以往一个时间点 (如实际的年、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.
