只用that不用which的7种情况
which通常引导非限制性定语从句，可直接放介词后作宾语。that先行词是much、little、none、the only和the same等词或被这类词修饰时、关系代词在定语从句中作表语时、避免重复时、先行词是既指人又指物的并列词组时。
只能用that，不能用which
1、先行词bai由all,much,little,few,something,anything,everything,none,nothing等不定代词修饰或先行词是不定代词本身。
例如 All that can be done has been done.
2、先行词有the only, the same, the very修饰时。
例如 The articles are the very ones that should be read.
3、先行词有形容词最高级时。
例如 This is the best film that I have ever seen.
4、先行词既指人又指物。
例如 We talked about the person and things that we remembered.
5、句中已经有who或which时，避免重复。
例如 Who is the man that is making a speech?
6、先行词被序数词修饰时
7、句子本身是Which 或Who引导的疑问句时