第1个回答 2013-10-07
因为since的意思是:自从
since不管用作介词、连词还是副词,句子(主句)谓语通常都用现在完成时。如:
I haven't seen her since last week. 自上周以来我一直未见过她
I met him in 1975 and haven't seen him since. 1975年我见过他,但自那以后就一直未见到他。
We have been good friends since we met at school. 自从读书相识以来,我们一直是好朋友。
注:表示时间长度时,通常用一般现在时代替现在完成时。如:
It's a long time since I met you last. 好久不见了。
It's about six months since we arrived here. 我们到这里大约有半年了。