一 定语从句中关系代词的使用
⒈ 如果修饰人,一般用关系代词who,whom,whose 或that.在定语从句中作主语的一般用who或that,作宾语的一般用whom,who或that,作定语并具有物主性质的用whose.（在定语从句中作宾语的关系代词可省略）
如：
①I don’t like people who/that get angry easily.
我不喜欢容易发脾气的人.
（ 关系代词who/ that在定语从句中作主语,不可省略）
②Here is the man (whom/ who/ that) you want to see.
这就是你想见的人.
（ 关系代词whom/ who/ that在定语从句中作宾语,可以省略）
③Is there anyone in your class whose home is in the northeast?
你班上有谁家在东北的?
（ 关系代词whose在定语从句中作定语,不能省略）
注意：用who 还是whom ,完全根据它们本身在定语从句中的地位和作用而定,与先行词在主句中的作用无关.尤其要注意在带有插入语的定语从句中who和whom的选用.
如：
①The person who sent the letter had to pay the postage.
寄信人要付邮资.
（ who sent the letter是定语从句,修饰person,who在定语从句中作主语,因此用主格）
②He is a man who I believe is honest.
他是一个我认为诚实的人.
（ I believe是插入语,去掉该插入语剩下的便是He is a man who is honest,在语法及句意上都能成立,who是定语从句中动词is的主语,故用主格,不用宾格whom.）
⒉ 如果修饰事物,用关系代词which 和that,作宾语时可省略.作介词宾语时,如果介词位于关系代词之前,则用which (不能省) ,而不用that（关系代词that既能代人,又能代物）.whose也可用来指物（此时可用of which来代替）,在定语从句中作定语.
如：
①Don’t buy tomatoes that/ which are green.
不要买颜色还是青的西红柿.
( that/ which 在定语从句中作主语,不能省)
②The fish (that/ which) they sell are not fresh.
他们卖的鱼不新鲜.
（ that/ which 在定语从句中作宾语,可以省）
③The classroom whose door is broken will soon be repaired.
= The classroom the door of which is broken will soon be repaired.
门坏了的那个教室将很快修理.
④The tool with which he is working is called a saw.
=The tool (that/ which) he is working is called a saw.
他干活用的那个工具叫叫锯.
（介词with位于关系代词之前,须用which,不能省,也不能用that）.