用that不用which的情况 先行词是all，much，few，little，everything，anything，nothing，none，the one等不定代词时 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 先行词是形容词的最高级或先行词前有形容词最高级修饰时 先行词是序数词或其前有序数词对其进行修饰时 先行词既指人又指物时 主句是who或which等引导的特殊疑问句时 用which不用that的情况 在非限制性定语从句中用which不用that 介词后边用which不用that 　　We should do everything that is useful to the people.

　　我们应该做一切有益于人民的事。

　　When we talk about Hangzhou，the first that comes into our mind is the West Lake.

　　我们谈论杭州时，首先想到的是西湖。

　　This is the smallest computer that can be found in the world now.

　　这是目前发现的世界上最小的计算机。

　　二、"介词＋关系代词"的用法

　　1．"介词＋关系代词"结构中介词的确定方法。

　　(1)根据从句中的谓语动词或主要的形容词确定介词。

　　The poor man has no house in which he can live.

　　那个穷人没房子住。

　　(2)根据定语从句修饰的先行词确定介词。

　　I don't know the reason for which he was late for school.我不知道他为何上学迟到。

　　(3)根据句子所要表达的意思确定介词。

　　This is the pilot by whom my son was saved.

　　这就是那位救了我儿子的飞行员。

　　2．"介词＋关系代词"结构中的关系代词通常用which或whom，不用that。

　　I'll never forget the day on which I joined the army.

　　我永远也忘不了我参军的那一天。

　　This is the pencil with which I draw pictures.

　　这是我画画用的那支铅笔。

　　3．关系副词where，when，why可替换成"介词＋which"，介词取决于先行词及介词＋which在从句中的作用。why只可替换for which。

　　This is the house in which I lived two years ago.

＝This is the house where I lived two years ago.