定语从句只能用that的情况包括：
(1).先行词为all, everything, anything, nothing, little, much,等不定代词时
He told me everything that he knows. 
他告诉我他知道的一切。
There is nothing that he can't do.
没有什么是他做不了的。
I don't have anything that is yours.
我没有你的东西。

(2).先行词被all, any, every, each, much, little, no, some, few等不定代词修饰时
All the books that you offered have been given out.
你提供的所有书籍都已被分发。
There is little water that is clean.
没有多少水是干净的。

(3).先行词有形容词最高级和序数词修饰时
This is the best film that I have ever seen.
 这是我看过的最好的电影。
[先行词含最高级，是定语从句只能用that的情况]
You are the kindest man that I have ever known.
你是我认识的最善良的人。

(4).先行词既指人又指物时
We talked about the persons and things that we remembered.
我们谈论了我们记得的人和事。
Can you see the girl and her cat that are sitting on the chair？
你能看见坐在椅子上的那个女孩和她的猫吗？

(5).先行词被the only, the very，the same, the last修饰时
He is the only man that I want to see.
他是我唯一想见的人。
She is the very girl that we are looking for.
她正是我们正在寻找的那个女孩。

(6).句中已经有who或which时，为了避免重复时
Who is the man that is making the speech?
那位正在演讲的男士是谁？
Which is the book that you need?
你需要的是哪本书？

总之，用that的范围比which/who更加广泛。
定语从句只用that口诀：
以下情况只用that，先行是个不定代，
或是含有不定代，含有最高级序数，
指人又指物，或有which/who，
别忘the very/only/last/same。

定语从句只能用that的情况就解析到这里，要学到更多，请点击：
定语从句用法