定语从句只能用that而不能用which的六种情况：
1、如果先行词是all, much, anything, something, nothing, everything, little, none等不定代词,关系代词一般只用that,不用which。如：
All that can be done has been done.
能做的都已经做了 。
He will tell you everything that he heard about it.
他将告诉你他所听到的关于这件事的一切。
2、当先行词被all, every, no, some, any, little, much所修饰时，只能用that，如：
There is little work that is fit for you.
没什么工作运合你做。
I have eaten all the food that is left.
我把剩下的所有食物都吃了 。
3、先行词是序数词或最高级形容词时，或者先行词被序数词（包括last，next)、最高级形容词及the only, the very等修饰时。如：
This is the first film that I have seen since I came here.
这是我到这里后所看的第一场电影。
This is the best that has been used against pollution.
这是用来防止污染的最好办法。
This is the very book that I am looking for.
这正是我一直在寻找的那本书。
4、先行词包括人和物时，关系代词应该用that。如：
They often talk about the people and the things that they are interested in.
他们常常谈论那些他们感兴趣的人和事。
Luxun and his works that we are familiar with are considered great.
人们认为我们所熟识的鲁迅及其作品都很伟大。
5、当主句是以who或which升头的疑问句时，为了避免重复，多用that导。如：
Which is the house that caught fire last night?
昨晚失火的是哪座房子？
Who is the lady that is playing the piano?
在弹钢琴的那位小姐是谁？
6、当先行词在定语从句中作表语时，只能用that。如：
This is a book that I have been looking for since last week.
这就是那本自上周以来我一直在寻找的书。
只能用that的情况：人物、高、序、不、避、恰
1、人物：先行词既有人又有物时；
They talked about persons and things that they met.
他们谈论他们遇到的人和事。
2、高：先行词被形容词最高级修饰时；
This is the most interesting film that I have ever seen.
这是我看过的最有趣的电影。
3、序：先行词被序数词修饰时；
He is the last man that I want to see.
他是我最不想见到的人。
4、不：先行词被不确定的数量词修饰（any, every, each, few, little, no, some, all等），或者先行词是不定代词（all, something, nothing, anything等）
Is there anything that you want to buy in the shop？
你想在店里买点什么吗？
5、避：当句中已经有who或which时，为避免重复，只能用that；
Who is the girl that is crying？
哭的那个女孩是谁？
6、恰：先行词被the only, the very, the same(“正是、恰恰是”)修饰时。
This is the only bike that I lost.
这是我唯一丢的自行车。
1、不定代词 anything, nothing, everything,all,much,few,any,little为先行词时；
Finally, the thief handed everything that he had stolen to the police. 最终，小偷偷的所有东西全部交给了警察。
2、先行词为 the only, the very, the just时；
He is the very man that helped the girl out of the water. 他从水中救起了那个女孩。
3、先行词为序数词、数词、形容词或最高级时；
The first English book that I read was "The Prince and the Pauper" by Mark Twain. 我读的第一本书是马克·吐温写的《王子与贫儿》。
4、先行词既有人又有物时；
He talked about the teachers and school that he visited. 他在讲他以前访问过的学校和老师。
5、当主句是以who或which开始的特殊疑问句时，为避免重复用that；
Who is the person that is standing at the gate? 那个站在门口的人是谁？
6、关系代词作表语时；
He is not the man that he used to be. 他以前不是这样的人。
扩展资料
1、先行词
之所以称它为先行词，是因为修饰它的定语从句总是放在它之后，先行词总是出现在定语从句之前，而不同于普通形容词修饰名词时，形容词位于名词之前。
Don’t forget the book that I told you to bring.（“the book”为先行词）别忘了把我让你带的书带过来。
2、关系词
引导定语从句。关系词根据其在定语从句中的功能可分为关系代词和关系副词。关系代词在定语从句中作主语、宾语、表语、定语等，关系副词在定语从句中作状语。
含有定语从句的句子一般分为两层：即主句层（第一层），定语从句层（第二层）。种类有常见的关系代词、常见的关系副词。
参考资料来源：百度百科-定语从句
4) 当先行词被序数词或形容词最高级所修饰时5) 在there be句型中，常用that.
(6) 先行词有两个，一个指人，一个指物，关系代词应该用that
1.当先行词是all,much,little,few,something,anything,everything,none,anything等不定代词或被它们修饰时。
2.当先行词是be后面的表语。
He isn't the man that he was.
The school is quite different from the one that it used to be.
3.当主句以here，there开头时。
4.当主句以who，which开头的特殊疑问句时。
5.当先行词有the only，the same，the very，the last等词修饰时。
6.当先行词是序数词，形容词最高级或者被它们修饰时。
7.当先行词有两个或两个以上，并且分别表示人和物时。
