全國公共英語考試語法—— since的四種用法

) 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.