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.

　　因為我們還年輕，所以不應該太害怕犯錯誤。

　�。�3）Since you are free today, you had better help me with my mathematics.

　　既然今天你休息，你最好幫我補習數學。

　　because的用法：

　　（1）We couldn't go out because these robber are still outside.

　　我們不能出去，因為這些強盜還在外面。

　�。�2）I do it because I like it.

　　我做這件事是因為我喜歡。

　　（3）You can trust those products because the quality never varies.

　　你可以信賴那些產品，因為它們的質量從來不變。

　　（4）We went by bus because it was cheaper.

　　我們乘公交汽車去，因為這樣便宜一些。