同学你好，该知识点来自沪江网校《中小学金牌新概念英语第三册【升级班】》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。

同学你好哦~
as可指其前后主句提到的事实或情况，因此引导的非限制性从句位置比较灵活，which可以放在主句前后，也可插入主句之中；而which引导的非限制性从句只能位于主句之后：
As is known to all, fish can’t live without water.
Air, as we know, is gas.
He saw the girl, which delighted him.

在非限制性定语从句中关系代词指代主句中某一个单词时，常用which：  
My brother enjoyed playing basketball , which he really plays well. Beijing , which he was born in, is our capital.

在非限制性定语从句中“介词+关系代词（介宾代物）”中关系代词只能用which  ：
The Travel Agency, with which our company has been dealing for several
以上，祝同学学习愉快~