1. 由as, which 引导的非限定性定语从句,as和which可代整个主句.

as引导的非限制性定语从句可以位于句首、句中和句末；which 引导的从句只能放在主句之后。如：

1) As is known, the earth goes around the sun.

= ________________________the earth goes around the sun.

= ____________________is that the earth goes around the sun.

2) He was badly ill, _________made him not go to school.

2. as有"正如，就像"之意， 如：as we know=as is well known "众所周知"，as is often the case "情况常是如此"，as is expected"就像所预料的样"，as is mentioned"像提到的样"，as is supposed"像人们想象的那样"， as is said"据说"，as is reported "像报道的那样"等。

3. 如果定语从句放在主句后，关系词作主语其后的动词是实义动词, 则用which.

1) He came late again, _________made his teacher angry.

2) Tom works hard at his lessons, _______is usual with him.

C. 介词+关系代词引导的非限定性定语从句

1. 介词+关系代词可以引导限定性定语从句和非限定性定语从句。该结构中关系代词指人时用 whom;指物时用which;不可用that；关系代词在从句中作定语时用whose。

1）He still remembered the day ____________he met Chairman Jiang.

2）The rat made a hole through which it could go out.

3) This is professor Smith, _____________you can learn a lot about biology.

2. 在介词前可加 all, some, none, half, most分数百分数，数词等。

1) I have many friends, some of whom (=of whom some) are teachers.

2) He has lots of books, many of which are about cartoon characters.

II. 关系副词引导的非限制性定语从句

1) We will put off the outing until next week, when we won't be so busy.

2) She is going to spend the summer holiday in America, where she has some relatives.

归纳拓展：

引导非限制性定语从句的关系副词有when和where.

注意: 非限制性定语从句一般不用why引导，常用for which替代why.

如：None of us accepted the reason he explained, for which he was absent.

即景活用：关系副词填空