英语六级基础语法知识：关系代词
1.指人的关系代词：who, whom, whose, that 的用法：
(1)作主语(who, that )
Those who are going to play in the match are to meet at the gate at 1:30 after lunch. 那些参加比赛的人午饭后1：30在大门口集合。
在本句中，先行词是those;关系代词who引导定语从句，同时代替先行词在从句中担任动词are going to play 的主语。
The man who/that is talking with Mr. Wang is a famous doctor. 正在和王先生说话的那个人是一个有名的医生。
在本句中，先行词是the man;关系代词who/that引导定语从句，同时代替先行词在从句中担任动词is talking的主语。
这个复合句可以还原成两个句子：The man is a famous doctor. He is talking with Mr. Wang.
(2)作宾语包括作介词宾语(whom, that )。此种情况下的关系代词可以省略;
This is just the man(whom/that) I want for the job.这正是我要的做这份工作的人。
在本句中，先行词是the man;关系代词whom/that 引导定语从句，同时代替先行词在从句中担任动词want 的宾语。
(3)当关系代词紧跟介词作介词宾语时，不能用that，也不能省略，
如：The book from which I got a lot of useful information was written by a famous scientist.
我从中得到许多有用信息的那本书是一位著名科学家写的。
但是当介词放在从句末尾时，作为介词宾语的关系代词可以用that 并且可以省略。
如上头两句可改为：
The book (that /which) I got a lot of information from was written by a famous scientist.
2.指物的关系代词which和that的用法：
(1)作主语
This is the instruction manual which/that tells you how to operate the computer. 这是那本教你如何操作计算机的说明手册。
(2)作宾语包括作介词宾馆。此种情况下的关系代词可以省略：
The chair (which /that) you broke yesterday is now being repaired. 你昨天弄坏的那把椅子现在正在修理。
The accounts of the company, (which/that) I’ve been paying great attention to, are in balance.
我一直非常注意的公司账目，是保持平衡的。
3.whose 和of which 指代人或事物，作定语。of which 可用whose 代替; The car whose lights (of which the lights/the lights of which) were all broken was my father’s.
那辆所有的灯都破了的汽车是我父亲的。
That is the book whose cover (of which the cover/the cover of which ) was broken. 这就是那本封皮破了的书。
4.关系代词的格应与它在从句中充当的成分一致。特别要注意插入语，
如：Peter is the one who everybody believes will fail to bring off the contract. Peter 是那个人人都认为不能完成合同的人。(everybody believes 是插入语) At the election I voted for the man whom I believed to be the most suitable. 在选举的时候我投了我认为最合适的那个人的票。
5.关系代词作从句的主语时，从句的动词必须和先行词的人称和数一致： 例：These are the operating instructions that/which are written in English 。 这就是用英文写成的使用说明。
6.非限定性定语从句不用that，只用who(whose, whom)和which代表人和物; 例：Her brothers, both of whom work in America, ring her up every week。 她的兄弟们两个人都在美国工作每个星期都给她打电话。
7.关系副词(=介词+关系代词)： 关系副词 先行词 在从句中的作用 说明 when(=at / on / in /during which),非正式文体中，有时用that代替关系副词
where(=in / at which) 地点名词 地点状语
why=(for which) 只有reason 原因状语
例：I shall never forget the day when (=on which) we first met. 我永远也不会忘记我们第一次见面的那一天。
From:https://www.zgghmh.com/CET-6/20007652.asp