英语“定语从句”“定语从句”是怎么回事?who,whose,whom,which在什么情况下用啊?

英语“定语从句”
“定语从句”是怎么回事?who,whose,whom,which在什么情况下用啊?

定语从句：英语中,在复合句中作定语,修饰主句中的某名词或代词的从句.
先行词：被定语从句所修饰的词,通常放在定语从句之前.
引导词：引导定语从句的词（也叫关联词）
关系代词：如that, which,who,whom,whose等
关系副词:如when, where, why等）.
引导词通常位于先行词和定语从句之间,它既起联系作用,又充当从句中的某个句子成分.
其间主要区别：
that与which的用法区别

两者都可指物,常可互换.其区别主要在于：
1. 引导非限制性定语从句时,通常要用which：
The current, which is very rapid, makes the river dangerous. 水流湍急,使这条河很危险.
He has to work on Sundays, which he doesn’t like. 他得在星期天工作,他是不喜欢这样的.
The London team, which played so well last season, has done badly this season. 伦敦队上一个季度打得很好,这个季度却打得很差.
2. 直接放在介词后作宾语时,通常要用which：
She may be late, in which case we ought to wait for her. 她可能晚到,那样我们就要等等她.
The documents for which they were searching have been recovered. 他们找寻的文件已找到了.
This morning some port wine came, for which I have to thank you. 今天早上送来一些波尔图葡萄酒,为此我得向你道谢.
注：有时“介词+which”引导的定语从句可以转换成“介词+which+不定式”结构：
He had only the long nights in which he could study. =He had only the long nights in which to study. 他只有漫漫长夜可用来学习.
He had a couple of revolvers with which he could defend himself.= He had a couple of revolvers with which to defend himself. 他只有一两把手枪用来自卫.
3. 当先行词是下列不定代词或被它们修饰时much, little, none, all, few, every(thing), any(thing), no(thing) 等时,通常用that：
All that she lacked was training. 她缺的只是训练.
Have you everything that you need? 你需要的东西都有了吗?
The sleeping man’s subconscious mind retained everything that was said around him. 这位酣睡的人头脑的下意识能记住他周围的人说的话.
She would never do anything that was not approved of by her parents. 她父母不赞同的事她绝不会做.
4. 当先行词有the very, the only, the same 等修饰时,通常用that：
This is the only example that I know. 我知道的例子只有这一个.
Those are the very words that he used. 那是他的原话.
5. 当先行词有形容词最高级或序数词(包括last, next等)等修饰时,通常用that：
This is the best dictionary that I’ve ever used. 这是我用过的最好的词典.
The first thing that you should do is to work out a plan. 你应该做的第一件事是订个计划.
6. 当关系代词在定语从句中用作表语时,通常用that：
China is not the country (that) it was. 中国已不是过去的中国了.
7. 当先行词是一个既指人又指物的并列词组时,通常用that：
They talked about the persons and things that most impressed them. 他们谈论了使他们印象最深的人和事.
8. 当要避免重复时：
Which is the course that we are to take? 我们选哪门课程?
that与who的用法区别
1. 两者均可指人,有时可互换（包括当先行词为 all, anyone, someone等,同时也包括先行词受the only等的修饰时）：
All that [who] heard him were delighted. 所有听了他讲话的人都很高兴.
He is the only one among us that [who] knows Russian.他是我们中间唯一懂俄语的人.
Anyone who [that] is over sixteen is allowed in. 任何超过十六岁的人都允许进去.
It is impolite to turn your back on someone who [that] is speaking to you. 人家跟你说话,你把背朝人是不礼貌的.
2. 但是在下列情况,通常要用 that：
①当先行词是一个既指人又指物的并列词组时：
I made a speech on the men and things that I had seen abroad. 我就我在国外所见到的人和事作了报告.
②当先行词是who时(为避免重复)：
Who was it that won the World Cup in 1982? 谁赢得了1982年的世界杯?
③当关系代词在定语从句中作表语时(可省略)：
Tom is not the boy (that) he was. 汤姆这孩子已不是以前那个样子了.
3. 但是在下列情况,通常要用 who：(www.yygrammar.com)
当先行词为 those 且指人时,英语习惯上要用 who 来引导定语从句.如：
Those who do not wish to go need not go. 不愿去的人不需要去.
Those who couldn’t walk were carried on stretchers. 那些不能走的人都用担架抬着.
It is said that those who eat the most are the least healthy. 据说吃得最多的人身体最差.
Only those who had booked in advance were allowed in. 只有那些预先订票的人可以进去.
The plan was supported by those who wished to listen to more good English. 这计划受到想多听好英语的人的支持.
Let us spend a few moments in silence so that / in order that we remember those who died to preserve our freedom. 让我们默哀片刻,以缅怀那些为维护我们的自由而牺牲了的人们.
注：偶尔也可见到在 who 之后用 that 引导定语从句的用例,但相当少见.如：
The danger is that people who pay their bills on time will be lumped in with those that don’t. 危险的是那些及时付账的人将会同那些不及时付账的人混在一起.（摘自《朗文当代英语辞典》2003年第4版）