Question

which引导的是定语从句， that引导的是什么呢？

Answer 1

which 可以引导一个非限制性定语从句，that 则不能，例如：
He had failed in the English, which made his father very angry.
Which 之前可以有介词，that 之前则不能，例如：
This is the house in which Tom used to live.

只能用that，而不能用 which 的情况

1.当先行词是all, everything, nothing, something, anything, much, little, few，none 等不定代词时，例如：
That is all that I want to say.

2. 当先行词被序数词或形容词最高级所修饰时，例如：
The first place that I visited in Beijing was the Great Wall.
This is the best film that I have ever seen.

3. 当先行词被 the very,the only,the just 等词修饰时，例如：
Mr. Smith is the only foreigner that he knows.

4. 当两个先行词一个指人,一个指物时，例如：
The famous writer and his works that the radio broadcast have aroused great interest among the students.

5. 当主句已有疑问词who或which时，例如：
Who that you have even seen can do better?
6. 如果有两个定语从句，其中一句的关系代词是 which ，另一句则用that，例如：
Let me show you the book that I borrowed from the library which
was newly open to us.