常用于现在完成时或过去完成时)自...以来,从...至今
I haven't heard from him since last year.
我自去年以来未曾收到过他的信.
(常用于现在完成时或过去完成时)自...以来,从...至今
It's been ten years since they married.
他们结婚到现在已经十年了.
She has been living a hard life since her husband died.
她自从丈夫死后,一直过着艰苦的生活.
既然;因为,由于
He must have taken the book since it isn't here.
他一定是把书拿走了,因为书已不在这里了.
Since it is so hot,let's go swimming.
既然天气这么热,我们去游泳吧.