同学你好，该知识点来自沪江网校《2020考研蜕变标准班【政英数+专业课一对一】【全额奖学金班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

一. as引导的非限制性定语从句位于句末时，一般可以和which互换。
The author was brought up in a small village, as (which) is recounted in some of his stories.
作者是在一个小村庄里长大的，这个问题在他的一些小说了就被提到过。
She is extremely popular among the students, as (which) is common knowledge.
她在学生中间很受欢迎，这是普遍知道的。
但是，当主句是否定句时，as和which就不能互换，因为as引导的非限制性定语从句不包含否定意义。
Spiders are not insects, as many people think.
蜘蛛不是昆虫，而许多人却认为蜘蛛是昆虫。
二. as引导的非限制性定语从句可以放在句子的中间，which引导的定语从句也可以放在句子的中间。
Water, which is a clear liquid, has many uses.
水是一种透明的液体，有许多用途。
Taiwan is, as you know, an inseparable part to China.
众所周知，台湾是中国不可分割的一部分。
三. as引导的非限制性定语从句可以放在句子的最前面，而which引导的定语从句不能放在句首。
As is often the case, the girl forgot to her dictionary.(不能用which)
经常是这样子的，那个女孩忘了带字典。
As you will find out, all is now settled.
你将会看到这样的情况，一切都已搞定了。