that 在限制性定语从句中既可指人又可指事或物。在下列情况下，只能用that 来引导定语从句：
1.
先行词被all, few, little, much, every, some, no等词修饰或被the only, the very, the same, the last 等
限定词修饰时。例如：
These are all the pictures that I have seen.
This is the very dictionary that is of great help.
2. 先行词是all , much, few, little, everything, anything, nothing 等
不定代词时。例如：
Is there anything that you want to buy?
3. 先行词既指人又指物时。例如：
My father and his teacher talked a lot about the things and the persons that they could remember.
4 主句是who 或which 引导的特殊问句时。例如：
Who is the girl that is standing under the tree?
Which is the machine that we used last Sunday?
5. 先行词被形容词最高级或
序数词修饰时。例如：
This is the best English film that I have ever seen.
The first English novel that I read was A Tale of Two Cities.
6.
关系代词在定语从句中作
表语时。例如：
Our school is not the one that it used to be