since的用法：
（1）Since the rain has stopped,let’s go for a walk.
既然雨停了，我們出去散散步吧。
（2）Since we are young,we shouldn’t be too afraid of making mistakes.
因?yàn)槲覀冞�年輕，所以不應(yīng)該太害怕犯錯(cuò)誤。
（3）Since you are free today, you had better help me with my mathematics.
既然今天你休息，你最好幫我補(bǔ)習(xí)數(shù)學(xué)。
because的用法：
（1）We couldn't go out because these robber are still outside.
我們不能出去，因?yàn)檫@些強(qiáng)盜還在外面。
（2）I do it because I like it.
我做這件事是因?yàn)槲蚁矚g。
（3）You can trust those products because the quality never varies.
你可以信賴那些產(chǎn)品，因?yàn)樗鼈兊馁|(zhì)量從來不變。
（4）We went by bus because it was cheaper.
我們乘公交汽車去，因?yàn)檫@樣便宜一些。