since/because

上面的 since 用得不对。连词 since 与连词 because 都可能引导原因状语从句，而且有时候也能够互换：

She's gone for a walk, $\$left\{ \begin{array}{l} because \\ since \end{array} \right\} the rain has stopped. (CGEL) 她出去散步去了，因为雨停了。

但是, since 从句与 because 从句有一个重大的差别: since 从句主要用来表达听者或读者已知的原因, 即表达已知信息。由于 since 从句的这一语义特点, 它就不可能成为信息的焦点, 不能回答 why? 的问题, 也不能用在强调句型中作为被强调的成分。

1. “Why do you have no electricity?” “Because there was a power failure.” (CGEL) “你们为什么没有电?”“因为电源发生了故障。”

2. It is because you are lazy that you lost your job. (CGEL) 正是因为你懒惰你才失掉了工作。

由于 since 从句常常表达听者或读者所已知的原因,因此,在多数情况下,它位于主句之前,而较少位于主句之后。

1. Since sharks are heavier than water, they must swim continuously or they will sink to the bottom. (TOEFL) 由于鲨鱼比水重，所以它们必须连续不断地游，才能不沉入海底。

2. Since you know Latin, you should be able to translate the inscription. (CGEL) 既然你懂得拉丁文，你就应该能够翻译这个碑文。

3. Since the rain has stopped, she's gone for a walk. 由于雨停了，她出去散步去了。

4. . . . since Mother was pregnant with me, they decided she should go home to Hope until they could get into the new house. (B. Clinton, My Life) ……当时母亲已怀上了我，因此父亲决定让母亲先回霍普镇，等新房子能住时再把母亲接回来。（《我的生活》）

since 与 because 的区别有点像汉语“由于”和“因为”的区别。