1. 只能用that,不能用which作先行词的情况 (1)先行词是不定代词或者先行词被不定代词所修饰时, 关系代词通常只用that, 不用which.例如: That’s all that I know. 我知道的就这些。 (2)先行词被序数词、 形容词最高级、 the only, the very, the last等修饰时, 关系代词通常只用that, 不用which.例如: This is the only thing that we can do now. 这是我们现在惟一能做的事情。 (3)先行词既有人又有物时, 关系代词只用that, 不用which.例如: The scientist and his achievements that you told me about are admired by us all. 我们所有人都钦佩你告诉我的那位科学家和他所取得的成就。 (4) 关系代词在限定性定语从句中作表语并带有类比含义时, 通常只用that, 不用which. 例如:Our school is no longer the school that it used to be. 我们的学校不再是以前的那所学校了。 (5) 句中其他位置已出现which, 为避免重复, 不用which而用that引导限定性定语从句。例如: Which is the car that has overtaken us? 超过我们的是哪辆车? 2. 只用which,不能用that作先行词的情况 (1) 在介词提前到关系代词之前形成“介词+关系代词”结构来修饰表事物的先行词时, 关系代词必须用which.例如: The house in which we live is very large. 我们住的房子非常大。 (2) 先行词为“those+表事物的复数名词”时, 关系代词通常只用which而不用that.例如: Students should keep in mind those regulations which restrict their behavior. 学生应牢记那些规范自己的行为准则。