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。