Question

不定式什么时候用as，和which的区别？

things,____is often the case,will turn out to be contrary to one's wishes.
此处为什么用AS。不用WHICH？在非限定性定语从句力WHICH和AS不是可以互换吗？
a good many proposals were raised by the masses,_____was to be expected.
此处为什么as和which可以互换？2个不都是非限定性定语从句吗？
还有as代替整个句子和整个主句是什么意思？

Answer 1

由which或as引导的非限制性定语从句，两者之间的区别在于：
1. which引导的定语从句只能位于主句后，但as引导的从句可位于主句前、中、后。如：
David, as you know, is a photograopher. 戴维是个摄影师，你是知道的。(不可用which)
Li Ming is late, as is often the case. 李明迟到了，这事是经常发生的。(不可用which)

2. as在定语从句中作主语时，从句谓语通常要有be或别的系动词，但which不受此限制。如：
Li Ming was late, which (=and this) made Mr. Zhang very angry. 李明迟到了，这件事使张先生非常生气。(不可用as)

3. as引导的定语从句只表示一个众所周知或意料之中的事，但which不受此限制。如：
He married her, which was unexpected. 他和她结婚了，这是出乎意料的。(不可用as)

4. as有“正如”之意，而which则意为“这(件事，一点)”，可用and this/that/it来代替。

5. as多用于固定搭配中：as is often the case(这是常有的事)，as was expected(不出所料)，as often happens(正如经常发生的那样)，as is known to all(众所周知)，as has been said before(如上所述)，as is mentioned above(正如上面所提到的)等。
注：which代表整个句子，还可用于in which case, at which point, on which occasion等。如：
I may have to work late, in which case I’ll telephone you. 我可能得晚点下班，那样我会给你打电话的。

祝你开心如意！