非限制性定语从句不能用why引导时，要用for which代替why.
如：
1、I had told them the reason, for which I didn't attend the meeting.
我已经把理由告诉了他们，为此我没有去开会。
2、I had told them the reason why I didn't attend the meeting.
我告诉了他们我不去开会的理由。(限制性定语从句“the reason why...”是常见搭配。)
扩展资料：
一、which作引导词的用法
关系代词which在非限制性定语从句，中所指代和修饰的可以是主句中的名词、形容词、短语、其他从句或整个主句，在从句中作主语、动词宾语、介词宾语或表语。
1、which指代主句中的名词，被指代的名词包括表示物、婴儿或动物的名词、表示单数意义的集体名词以及表示职业、品格等的名词。
如：These apple trees，which I planted three years ago，have not borne any fruit.
这些苹果树是我三年前栽的，还没有结过果实。
2、which指代主句中的形容词。
如：She was very patient towards the children，which her husband seldom was.
她对孩子们很耐心，她丈夫却很少这样。
3、which指代主句中的某个从句。
如：He said that he had never seen her before，which was not true.
他说以前从没见过她，这不是真的。
4、which指代整个主句。
如：In the presence of so many people he was little tense, which was understandable.
在那么多人面前他有点紧张，这是可以理解的。
二、注意事项
1、which引导的非限定性定语从句是用来说明前面整个句子的情况或主句的某一部分。
2、as有时也可用作关系代词 。as引导非限制性定语从句，若as在从句中作主语，其引导的句子可以放在句首，也可以放在句中。但which引导的非限制性定语从句只能放句中。
例句：
As is reported in the newspaper ，some artistic treasures(艺术珍品） will be on show at the exhibition （展览品）on the weekend.
据报纸报道，一些艺术珍品（艺术珍品）将于周末在展览（展览品）上展出。
3、在非限定性定语从句中，关系词不能用that,和those。
参考资料来源：百度百科-非限制性定语从句
关系副词含义相当于”介词＋which结构”,因此常常和”介词＋which”结构互换
其中
关系副词有：when,where ,why
介词＋which结构有：
when =in/on which ,where=in/at which ,why =for which
that \which在代物时常常可以通用,但有时只宜于用which ,不用that
(1) 关系代词前有介词时.
This is the hotel in which you will stay.
(2) 如有两个定语从句,其中一句的关系代词是that,另一句宜于用which.
Let me show you the novel that I borrowed from the liberary which was newly open (新开放) to us.
注意2that \which在代物时常常可以通用,但有时只宜于用that ,不用which.
(1) 先行词是形容词最高级或者它的前面有形容词最高级时
This is the best that has been used against air pollution(反对空气污染) in cities.
English is the most difficult subject that you will learn during these years.
(2) 先行词是序数词,或它的前面有一个序数词时
He is the last person that I want to see.
(3) 主句中已有疑问词时
Which is the bike that you lost?
(4) 先行词既有人又有物时
The bike and its rider that had run over (撞倒了)an old man were taken to the police station.
(5) 先行词是all,much,little,something,everything,anything,nothing,none,the one等代词时
You should hand in all that you have.
We haven’t got much that we can offer you.
I mean the one that you talked about just now.
(6) 先行词前面有only,any,few,little,no,all,one of,the same,the very等词修饰时
The only thing that we can do is to give you some money.
Li Ming is the only one that got full marks (满分)in our class.
Li Ming is one of the students that want to be teachers in our class.
(7) 有两个定语从句,其中一个关系代词已用which,另外一个宜用that
Edison built up a factory(办了一个工厂) which produced things that had never been seen before.
定语从句的关系副词 Where的用法:若先行词指地点且其在定语从句中充当地点状语.
This is the house+I was born in the house. (=I was born there)
介词短语 副词
=This is the house where I was born.这就是我在那儿出生的房子.
先行词 关系副词
in which I was born.
介词+关系代词
which I was born in.
关系代词
这里作介宾的which和that可以省略
that I was born in本回答被提问者采纳
