1) since +過去一個時間點 (如具體的年、月、日期、鐘點、1980, last month, half past six)?！?I have been here since 1989. 2) since +一段時間+ ago I have been here since five months ago. 3) since +從句 Great changes have taken place since you left. Considerable time has elapsed since we have been here. 4) It is +一段時間+ since從句 It is two years since I became a postgraduate student.