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. 先行词是all , much, few, little, everything, anything, nothing 等不定代词时。例如：
Is there anything that you want to buy?
2. 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.
My father and his teacher talked a lot about the things and the persons that they could remember.
Our school is not the one that it used to be.
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. 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?