sa之前要有先行词，b关代在从句中做主宾表，c否则前面有介词。
范围太大/无逗号/给限制。"……的"
He is a boy who works hard.他是个用功的男孩。
非限制性定语从句。
专有名词/已唯一/逗号，/非限制。
This is my mother, who loves me very much.这是我妈妈，她很爱我。
名词前已经有形容词修饰的，都可以用。
He is a good boy who studies hard.
He is a good boy ,who studies hard.
他是个用功的好孩子。
他是个好孩子，很用功。
限制性定语从句中，关代可省略。
关系代词为及物动词的宾语时。
This is the boy whom I saw yesterday.
This is the boy I saw yesterday.
关系代词为介词的宾语时，介词移至句尾。
This is the house in which he lives.
This is the house he lives in.
a.that只能出现在限制性定语从句中
b.that之前不能有介词。
a.序数词之后
b.最高级之后
c.""the very+名词""后。不需要翻译出来。
d.all之后,that作宾语时可省略。
all (that) he said is true.
Everything (that) he said is true.
e.""the only+名词""后。
f.避免重复第二个关代用that取代。
g.关代在be后作表语时。不能用who或which。
He is not the man who he once was. 错
He is not the man that he once was.对
i.两个名词性质不同，共用一个关代时。
Look at the boy and the dog that are coming this way.
i.避免与疑问词重复。
a.删除关系代词
b.之后的动词变成现在分词
c.若动词为be动词,变成现在分词being之后,可将being省略。
The girl who danced here yesterday is my sister. 主
The girl dancing here yesterday is my sister.
Who is that boy that is standing over there. 主
Who is that boy standing over there.
I like the car which is parked in front of the post office.
I like the car parked in front of the post office.→being parked
Who/which+be+n
I met joy, who is a good friend of mine.
I met joy, a good friend of mine.
He has no house in which he can live.
He has no house to live in.
Lend me your pen with which I can write my address.
Lend me your pen to write my address with.
关系代词所有格
whose可以代替人或物。
之前要有先行词，之后的名词作定从的主/宾。（的什么做主/宾）
代替物的时候，可用of which替代。
Whose color.
The color of which.
Of which the color.
关系副词
一共有四种，均由"介词+关系代词which"变化而成。
Where(= in which, on which,at which)
when(= in which, on which,at which)
why(=for which)
how(=in which)/the way
关系副词使用要点
1.省副词：在修饰限定的定语从句中，除where外，when及why可以省略，how看情况。
I shall never forget the day (when) she came.
That‘s the reason (why)he left.
2.省名词：当Where, when, why, how所修饰的名词在be动词之后作表语，可以省略该名词。
That‘s (the place) where he was born.
than, as和but基本连词,还可以作准关系代词.
Than,as,but作准关系代词条件是：前面必须有先行词（名词）
than = than + the + 前面的名词 + 关系代词（who, whom, which）
通常出现在more …than,less…than, fewer…than等结构中，且在从句中可以充当主语，宾语和be动词后得表语。
例1. I have more money than is needed.（than作从句的主语）
= I have more money than the money which is needed
例2. I have more money than he needs（than作从句的宾语）
I have more money than the money which he needs.
例3. he is a better student than you（ are ）.(than 作从句的表语)
as = as + the + 前面的名词 + 关系代词（who, whom, which）
在所引导的从句中作主语，宾语和be动词之后的表语。
注意：
① such + n. 之后不可用like（像）加以修饰。
Such a man like him is bad. (错)
Such a man as him is bad.（对）
② as 可替代主句。单独使用as时，as也可以作关系代词，等于which，用来代替整个主句。
He is nice, which is known to us
= he is nice , as is known to us(他人很好，我们都知道)
③ as引导的从句可置于主句的前后，而which引导的从句只能置于主句之后。
例. He is nice, as we all know= as we all know, he is nice
④只能与单数可数名词使用的结构。
即there is no + 名词 + who(whom, which, that)…not
= there is no + 名词 + but……
注意：
定语从句中有be 动词保留be动词
例：there is no one who is not interested in it.
= there is no one but is interested in it(没有人不对他感兴趣)
定语从句中有助动词（can,will,may,should…）保留该助动词。
There is nothing that he can not do
=There is nothing but he can do（没有什么事是他做不来的）
定语从句中有do,does和did等助动词时，先去掉助动词，再依时态人称将之后的动词还原。
There is no book which he doesn‘t like to read
= There is no book but he likes to read.
复合关系代词
由两个词类复合而成，先行词和关系代词。因此前面不能有先行词。
I don‘t believe the words what he said.错
I don‘t believe the words which he said.对
I don‘t believe what he said.对
代替人
Whoever = anybody who
Whomever = anybody whom 凡是……的人
代替人或物
Whichever
=any one which/who三者以上中的任一个。
=either which/who两者中的任意一个。
代替物
what = the thing(s) which
Whatever = anything which/that
Whichever, 指同一类的任一项。
whatever.只不同类的任一项。
Whatever/whoever也可以做副词连词。
复合关系代词，无逗号，作主宾表。
-----Whatever｜
Anything that｜he says is a lie.任何事
------Whoever｜
Anybody who｜makes the mistake should be punished.任何人
副词连词，有逗号，连接从句。
-------Whatever｜
No matter what｜he says, it‘s a lie.无论什么
-------Whoever ｜
No matter who｜makes the mistake, he should be punished.无论谁
原文：https://www.cnblogs.com/yeyeye123/p/10806936.html