当介词：
since 表示明确的日期或时间,时态常用完成时：
He’s worked here since 1980. 自从1980年他就在此工作.
She’s been sitting in the waiting room since two-thirty. 自两点半她就坐在等候室了.
当连词
引导时间状语从句
Since she married me, we had been happy. 自从她嫁给我以来,我们一直很幸福.
since引导原因状语从句：
•Since you don’t want to go, we won’t force you to. 既然你不愿意去,我们也不勉强你.
Since you are leaving tomorrow, we can eat dinner together tonight.
既然你明天要走,我们今晚一起吃晚饭吧.