文档介绍：as 和which引导非限制性定语从句的区别
1.                        as引导的非限制性定语从句
1)     位置灵活，可以置于主句的句首、句中或句末；
2)     先行词不可是一个词，必须是整个主句或主句的部分内容；
3)     有“正如、像”等意思，表依据、评论（、态度、看法）等；如：  
a.      This elephant is like a snake，as anybody can see．像任何人都能看见那样，这头象像条蛇。
b.     He failed in the exam, as we had expected.
c.         Tom has passed the test, as everybody knows. 正如每个人所了解的那样，汤姆通过了考试。
【比较：Bamboo is hollow，which makes it very light．竹子是空的，这就使得它很轻。】
4)        常用以下谓语动词的主、被动语态：know, see, say, expect, imagine, hope, believe, announce, suggest, report, point out…, 例：
a.         主动（做宾）：as we all know, as you know, as everybody knows; as you see, as we can see, as we have seen, as anybody can see; as was expected; as we can imagine, as we have imagined…
a)         As we all know, the earth is round.
b)        He was a foreigner, as I know from his accent.
c)     Mike, as we expected, attended the meeting．像我们所期望的那样，迈克参加了会议。
b.         被动（做主）：as is known to everybody, as is known to all; as has been expected; as is often the case (with …)，as has been pointed out, as is usual with, as is reported in the newspaper…
a)         He is an honest man, as is known to all.
b)        As is often the case with young people, he was overconfident.
c)     He wasn't unconscious，as could be judged from his eyes．他并未失去知觉，这从他的眼神可以判断出来。
2.    which引导非限制性定语从句
1)    只能置于句中或句末（即不可置于句首，只能置于先行词之后）；
2)    先行词即可是一个