as:由于,鉴于.主从并重,从句说明原因,主语说明结果.
for:因为,由于.表明附加或推断的理由,引导的分句前常有逗号,for分句不放句首.
since:因为,既然.侧重主句,主句表示显然的或已知的理由.
because:因为.表直接原因,回答why的提问;一般放在主句之后,也可单独存在.
because of:后面只能跟名词性的词语.
by:表示通过某种手段,由于某些特定的原因.because语气最强,since其次,as最弱区别a because表示直接理由.强调别人未知的事实,而since,as引导的原因状语从句一般表示已知的事实,强调引起的后果.例如：He had to to a part-time job after work because he needed money for his marriage.他下班后还得兼职因为他结婚需要钱.Since you know you are wrong,you had better admit it.既然你知道你错了,你最好赶快承认.As he couldn't express himself freely,he had to make some gestures.由于他不能表达自如,只得用手势.尤其在讯问尚未确定的原因时,必须用because.例如:Did he buy many books becasuse he was fond of reading?他买许多书是因为他喜欢看书吗?b.because引导的从句可以带修饰语just,only,也可以用于强调据或not.but并列结构,但since,as不可以.例如:The girl learned to play the piano not because she liked to play the piano but because her parents forced her to.女孩子弹钢琴不是因为她喜欢弹琴,而是因为她父母强制她学.
