A as（＝when／while）的用法的限制

这里as主要与表示动作或发展过程的动词连用，一般情况下它不与第168节中所列的动词连用，除如上面B3所示有发展之意时例外。在一般情况下它也不与live，stay，remain这类动词连用。

B as与上述动词或同类动词连用时，一般均表示because／since （由于）：

As he was tired…相当于：

Because he was tired...

因为他太累了……

As he knew her well…相当于：

Because he knew her well……

因为他了解她……

As it contains alcohd...相当于：

Since/Because it contains alcohol……

因为它含有酒精……

As he lives near here…相当于：

Since／Because he lives…

因为他住的地方离这儿很近……

C as与多数动词连用时，可以是两种意思中的任一个意思：

As/While he shaved he thought about the coming interview．

他边刮胡子，边想着即将进行的面谈。

As／Because he shaved with a blunt razor he didn’t make a very good job of it．

因为他用一把钝剃须刀刮胡子，所以刮得不好。

如果在这个问题上没有把握，最好用while或because。

D as+名词时意为when/while（当……时）或because/since（由于）：

As a student he had known great poverty．相当于：

When he was a student he had known great poverty．

他当学生时，经历过很贫困的生活。

As a student he gets/got in for half price．相当于：

Because he is／was a student be gets／got in...

由于是学生，他付半价就入场了。

As a married man，he has to think of his family．相当于：

Because／Since he is a married man...

作为一个有妇之夫，他必须考虑他的家庭。

as在这里意为 when／while时，后面常跟完成时态。

as意为because／since时，后面可跟任一时态。