2．定语从句在选择关连词that 与which时，常常容易出错，所以应记住什么时候只能用that，什么时候只能用which. （1）．只能用 that 的情况归纳4种：即先得词被序数词最高级修饰过；先行词为all 、everything、nothing等不定代词；先行词同时是人和物并列时；最后先行词分别被the only 、the very the same、the last 修饰。请看下列四组例句，注意其先行词： ①．The first thing that we should do is to work out a plan . ②．I t almost seemed as if the good man were trying to teach us all that he knew at this lesson . ③．Later my father and Mr.Crosset talked for about half an four of things and persons that they remembered in school. ④．This is the very dictionary that I want to find . （2）．只用which is 情况有两种情况：一是非限制性定语从句，关连词要用which；二是做介词宾语时只能用which。请看下列两组例句： I said nothing , which made him more angry . I have the book about which you are talking . 你的问题涉及到限定性定语从句和非限定性定语从句。 限定性定语：紧跟在先行词后面。 非限定性定语从句：逗号隔开，修饰前面的先行词，或者整句话。具体情况具体分析。

　　定位定语从句的先行词，除了要分析从句是否缺失主干成分之外，还要按照句子的意思来进行判断，一定要把先行词还原到从句当中去，句子意思合理才可以。

　　最简单的方法：看从句缺什么成分。 。 如果仅仅是想区分主语或宾语，还有一种简便的方法，就是看关系词后是什么词性的词，后面是名词（主语）的话先行词就是宾语，是动词（谓语）的话先行词就是主语。 如： 1.Father is talking to the man that has stayed here for a long time. 句中that后是谓语动词，所以that就充当主语，可以用who来代替。 2.Father is talking to the man that we are afraid of. 句中that后是名词（主语），所以that就充当宾语，可以用whom来代替。

　　限定性定语：紧跟在先行词后面。 非限定性定语从句：逗号隔开，修饰前面的先行词，或者整句话。

　　限定性定语：紧跟在先行词后面。 非限定性定语从句：逗号隔开，修饰前面的先行词，或者整句话。

　　限定性定语：紧跟在先行词后面。 非限定性定语从句：逗号隔开，修饰前面的先行词，或者整句话。

　　最简单的方法：看从句缺什么成分。 比如： 1.He is the policeman who caught the thief the other day. 去掉who后，从句缺主语：caught the thief the other day.所以who充当主语。 2.He is the policeman that I met yesterday. 去掉that后，从句缺宾语：I met yesterday.所以that充当宾语。 3.I like the book whose cover is dark green. 去掉whose后，从句缺定语：(Its) cover is dark green.故whose充当定语。 4.The temple where he used to live has been destroyed. 去掉where后，从句缺状语：He used to live (in the temple).故where充当状语。 如果仅仅是想区分主语或宾语，还有一种简便的方法，就是看关系词后是什么词性的词，后面是名词（主语）的话先行词就是宾语，是动词（谓语）的话先行词就是主语。 如： 1.Father is talking to the man that has stayed here for a long time. 句中that后是谓语动词，所以that就充当主语，可以用who来代替。 2.Father is talking to the man that we are afraid of. 句中that后是名词（主语），所以that就充当宾语，可以用whom来代替。