because語氣最強(qiáng),since其次,as最弱
區(qū)別
a because表示直接理由.強(qiáng)調(diào)別人未知的事實(shí),而since,as引導(dǎo)的原因狀語從句一般表示已知的事實(shí),強(qiáng)調(diào)引起的后果.
例如：
He had to to a part-time job after work because he needed money for his marriage.他下班后還得兼職因?yàn)樗Y(jié)婚需要錢.
Since you know you are wrong,you had better admit it.既然你知道你錯(cuò)了,你最好趕快承認(rèn).
As he couldn't express himself freely,he had to make some gestures.由于他不能表達(dá)自如,只得用手勢.
尤其在訊問尚未確定的原因時(shí),必須用because.例如:
Did he buy many books becasuse he was fond of reading?他買許多書是因?yàn)樗矚g看書嗎?
b.because引導(dǎo)的從句可以帶修飾語just,only,也可以用于強(qiáng)調(diào)據(jù)或not.but并列結(jié)構(gòu),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.女孩子彈鋼琴不是因?yàn)樗矚g彈琴,而是因?yàn)樗改笍?qiáng)制她學(xué).
It was because he lost it that he found it more valuable than ever.正因?yàn)樗チ怂?他才比以往任何時(shí)候感到它的寶貴.