定语从句是非常重要的一个语法点，明确什么时候用什么样的关系代词和关系副词非常重要。一般情况下，当先行词是人的时候用who和whom，当先行词是物的时候，用which，而that一般是都可以用，当然也有一些例外，下面是只能用that引导定语从句的十三种情况。
01句子的主语是先行词，而且又是物
在there + be 的句型中，句子的主语是先行词，而且又是物。例如：
There are two novels that I want to read. 我要读的有两本小说。
There is no work that can be done now. 没有什么工作现在能做的了。
02先行词为主句的'表语或关系代词为从句的表语
当先行词为主句的表语或者关系代词为从句的表语时。例如：
This is the book that was bought yesterday.这就是昨天买的书。
Our school is no longer the school that itused to be. 我们的学校不再是以前的学校了。
03以Here is (are)开头的句子时
以Here is (are)开头的句子时。例如：
Here is a film that will move anyone.这是一部将使任何人受感动的电影。
Here are two books that I will buy.这是我要买的两本书。
04It is (high)time +定语从句时
It is (high)time +定语从句时。例如：
It is time that we should have a rest.我们应该休息了。
It is high time that they started out. 他们该动身了。
05先行词是way，关系代词用that或者in which
当先行词是way等词时，关系代词用that或者in which在定语从句中作方式状语时，在口语中，常可省略。例如：
This is the way that my father did thiswork.这就是我父亲做此工作的方式。
She admired the way in which I answered thequestions. 她羡慕我回答问题的方式。
06双重限定性定语从句中，如果一个从句用who或者which引导时，另一个从句用that引导。
在双重限定性定语从句中，如果一个从句用who或者which引导时，那么另一个从句用that引导。例如：
He is the student that I have ever see whocan jump highest.他是我曾经看到过跳得最高的学生。
My brother studies in the school which isthe most beautiful in our city that isn’t far from here. 我的弟弟在我们的城市最美丽的学校读书，并且离这儿不远。
07当先行词被the last , thevery 和the only修饰时
当先行词被the last , thevery 和the only修饰时。例如：
This is the very pen that I am looking for.这正是我找的钢笔。
The only book I want to read is missing. 我唯一想看的书不见了。
08在强调句子中，并且以who ,which,what开头时
在强调句子中，并且以who ,which,what开头时。例如：
Who was it that was lost ? 究竟是谁迷路了？（此句中，最好不用who来代替that，避免重复。）
What was it that you did last week? 你上周究竟做什么了？
09当先行词有序数词时
当先行词有序数词时。例如：
You are the first person that I want to askfor.你是我要见的第一个人。
This is the second book that I have everwritten.这是我写的第二本书。
10先行词被all, every, no ,some, few , 等词修饰时
当先行词被all, every, no ,some, few , little, much, both等修饰时，例如：
This is all that I want to say at themeeting.这就是我在会上要说的。
Have you any books that are worth reading? 你有值的看的书吗？
11当先行词既指人又指物时
The professor and his achievement that Iheard about are admired by them .我听说的那位教授和他的成就得到他们的赞美。
Let’s talk about thepersons and the things that we can remember.让我们谈论能够想起的人和事。
12当先行词为anything、everything、nothing时
当先行词为anything、everything、nothing时，关系代词用that,不用which；但用something时，用which或者that均可。例如：
Everything we have seen in China is moving. 我们在中国看见的东西件件感人。
I have nothing that is worth reading. 我没有什么值得一读的东西。
13当先行词是疑问代词who时
当先行词是疑问代词who时。例如：
Who that you have ever seen can beat him inchess? 你曾见过谁能在棋艺上打败他？
