since是一个从属连词,它可以引导时间状语从句‘原因状语从句和方式状语从句等,从句既可置于主句之前,亦可置于主句之后．
1．从属连词since引导时间状语从句,意谓”自从.以来”．since引导的时间状语从句有两种用法：
第一种是从句用现在完成时,从句用一般过去时,表过去某个时间开始直到现在．如：
（1）I have not laughed since I became deaf .自从我聋了以后我就没有大笑过．
（2）It's been years since I enjoyed so much as last night .我已经好多年没有像昨晚那样痛快了．
since经常用ever加强语气．如：
（3）We've been friends ever since we met at school .我们自从同校相识后就一直是朋友．
第二种是主句用过去完成时,从句用一般过去时或过去完成时,表过去某个时间知道过去某个时间．如：
（4）Since she came to me ,we had been happy .自从她来到我这里,我们一直很快活．
（5) Two weeks had passed since Martin had seen him .自从马丁见到他以后,两周已经过去了．
2．从属连词since引导原因状语从句,意谓”既然”‘”因为”‘”由于”．如：
（6）Since you are going ,I will go too .既然你要去,我也要去吧．
（7）Why do people come to his lectures since he is difficult to understand 既然他的话难听懂,为什么人们还要来听他的演讲呢?
（8）Aircraft noise is a particular problem here since we're close to Heathrow Airport .由于我们*近希思罗机场,这里的飞机噪声就成了一个严重的问题．
3．since亦可用作介词．如：
（9）We hadn't seen each other since Oxford .我们自从牛津别后就彼此没有见过面．
(10) I have not heard from him since writing last .自上次写信以后,我没接到过他的信．
与after和before一样,since既可用作从属连词,亦可用作介词．但是这三个词后跟的-ing形式,必须看作介词和动名词组合,不能看作从属连词引导的省略分句,因为这里的-ing形式可以用物主代词修饰．如：
（11) Since my coming to London ,I have not been well.自从我来伦敦以后就一直没有好过．
4．since亦可用作副词．如：
（12) Her husband died ten years ago but she's since remarried .她的丈夫于十年前去世,但是她后来又结婚了．
（13) He came to England three years ago and has lived here ever since .他三年前来到英国,从那以后就一直住在这里． since是一个从属连词,它可以引导时间状语从句‘原因状语从句和方式状语从句等,从句既可置于主句之前,亦可置于主句之后．
1．从属连词since引导时间状语从句,意谓”自从.以来”．since引导的时间状语从句有两种用法：
第一种是从句用现在完成时,从句用一般过去时,表过去某个时间开始直到现在．如：
（1）I have not laughed since I became deaf .自从我聋了以后我就没有大笑过．
（2）It's been years since I enjoyed so much as last night .我已经好多年没有像昨晚那样痛快了．
since经常用ever加强语气．如：
（3）We've been friends ever since we met at school .我们自从同校相识后就一直是朋友．
第二种是主句用过去完成时,从句用一般过去时或过去完成时,表过去某个时间知道过去某个时间．如：
（4）Since she came to me ,we had been happy .自从她来到我这里,我们一直很快活．
（5) Two weeks had passed since Martin had seen him .自从马丁见到他以后,两周已经过去了．
2．从属连词since引导原因状语从句,意谓”既然”‘”因为”‘”由于”．如：
（6）Since you are going ,I will go too .既然你要去,我也要去吧．
（7）Why do people come to his lectures since he is difficult to understand 既然他的话难听懂,为什么人们还要来听他的演讲呢?
（8）Aircraft noise is a particular problem here since we're close to Heathrow Airport .由于我们*近希思罗机场,这里的飞机噪声就成了一个严重的问题．
3．since亦可用作介词．如：
（9）We hadn't seen each other since Oxford .我们自从牛津别后就彼此没有见过面．
(10) I have not heard from him since writing last .自上次写信以后,我没接到过他的信．
与after和before一样,since既可用作从属连词,亦可用作介词．但是这三个词后跟的-ing形式,必须看作介词和动名词组合,不能看作从属连词引导的省略分句,因为这里的-ing形式可以用物主代词修饰．如：
（11) Since my coming to London ,I have not been well.自从我来伦敦以后就一直没有好过．
4．since亦可用作副词．如：
（12) Her husband died ten years ago but she's since remarried .她的丈夫于十年前去世,但是她后来又结婚了．
（13) He came to England three years ago and has lived here ever since .他三年前来到英国,从那以后就一直住在这里．