定语从句中,whom只能在从句中充当宾语成分,who既可当主语又可当宾语.但是若是介词后的宾语,只能用whom而不能用who.
如：there is nobody who/whom he can turn to for help.没有谁可以让他寻求帮助.这里引导词当宾语,who和whom都行,当然这里既可指人也可指物的that也可以。
但是：there is nobody to whom he can turn for help.这里引导词同样当宾语,但是位于介词to后,只能用whom,而不能用who（that同样不行）。
扩展资料
定语从句中易混淆的难点
1、在限定性定语从句中指代物时，which 和that 一般可通用。
The new house that/which I has just bought is about six miles away.
They planted some trees that /which did n't need much water.
2、限定性定语从句中只用that 而不用which 的情况。A）先行词有形容词最高级修饰时 This is the best way that has been used against pollution. Polly is the most direct young woman that I have ever come across .
B) 先行词有序数词修饰时 This is the third time that they have met. The very first time that Lester saw the film, he made up his mind to become a doctor.
参考资料百度百科-定语从句
定语从句中Who和Whom的区别：
1、定语从句中，指人的先行词我们用who或者whom做连接词，who用来做从句的主语，whom用来做从句的宾语。
2、This is a nurse who wears a white skirt，文中连接词who都做下文的主语，此时我们用who是最为恰当的。
3、而在连接词做下文的宾语时，更多的是用whom，She is a teacher whom I like best。
拓展资料
主格
主格是指名词的语法的格。主格通常表示主格在拉丁语和古英语中都有。现在的英语中仍然存在于与宾格相反的主格代名词：I、you、we、he、she、it以及they。古英语的用法包括ye以及单数第二人称代词thou。
示例
I am a teacher.(主格作主语）
Please call me Jim. (宾格作句子的宾语）
Who is knocking at the door? It's me.（宾格作句子的表语）
My brother is an engineer.(形容词性物主代词作定语）
Ours is a big country.（名词性物主代词作主语）
You use yours and I use mine.(名词性物主代词作宾语）
定语从句中Who和Whom的区别：
1、定语从句中，指人的先行词我们用who或者whom做连接词，who用来做从句的主语，whom用来做从句的宾语。
2、This is a nurse who wears a white skirt，文中连接词who都做下文的主语，此时我们用who是最为恰当的。
3、而在连接词做下文的宾语时，更多的是用whom，She is a teacher whom I like best。
拓展资料
Who的用法
1、Who's there?
谁在哪儿？
2、Police have not been able to find out who was responsible for the forgeries
警方还未能查明谁是这些造假案的元凶。
3、There are those who eat out for a special occasion, or treat themselves
有些人会在特殊的日子或犒劳自己时出去吃饭。
4、Who is the least popular man around here?
这里谁最不受欢迎？
5、Who do you work for?
你为谁工作？
6、Who do you suppose will replace her on the show?
你觉得谁会代替她参加这场演出？
7、'You reminded me of somebody.' — 'Who?'
“你让我想起了一个人。”——“谁？”
8、I went over to start up a conversation, asking her who she knew at the party
我凑过去搭讪，问她这个聚会上都认识谁。
9、You know who these people are.
你知道这都是些什么人。
10、The woman, who needs constant attention, is cared for by relatives
那个需要长期照料的女人由亲戚们照看着。
11、The hijacker gave himself up to police, who are now questioning him.
劫持者向警方自首了，目前警方正在审讯他。
Whom的用法
1、Whom would it profit to terrify or to kill James Sinclair?
恐吓或者干掉詹姆斯·辛克莱对谁会有好处？
2、From whom shall I get comfort?
我从谁那儿能得到安慰呢？
3、About six thousand people were arrested, several hundred of whom have since been released
约6,000人被捕，后来其中的几百人又被释放了。
4、Being there gave me a chance to touch base with three friends whom I had not seen for a year.
在那里，让我有机会和一年没见面的三个朋友取得了联系。
5、What would I do? Whom would I run to? Momma was still away
我该怎么办？我能向谁求助？妈妈还没回来。
本回答被网友采纳Is he the man who/that wants to see you? 他是那个男人想见你？（who/that在从句中作主语）
He is the man whom/ that I saw yesterday. 他就是我昨天见的那个人。（whom/that在从句中作宾语）
此时，先行词在从句中作主语成分，只能用who,而不能用whom
2、例：He is one of the students to whom i have talked
当介词提前，介词后必须用且只能用whom
3、例：Gina ,who lives in China is my friend.
当定语从句为非限制性定语从句时，只能用who。
4、例：Do you know the person whom\who\省略不写 i talked to
当先行词在从句中作宾语成分时，whom who 都可以，也可以省略不写。