当定语从句修饰的词是不定代词，如anybody， nobody， nothing等，或是有only， very， 形容词最高级等修饰的名词时，从句的关联词往往用that ， that作从句的主语或宾语，作宾语时常被省略。

　　Is there anything (that ) I can do for you?

　　All(that) you have to do is to close the door and wait for him.

　　This is one of the easiest questions that do not need answering.

　　There is no one in the world who/that does not make a mistake.

　　定语从句修饰的词是不定代词、only、very、形容词最高级关联词用that，如果that在从句中做宾语，则可以省略。

　　3)修饰时间、地点、原因的定语从句

　　修饰时间的用when，相当于相当于“介词+ which”，在句中做状语。

　　修饰地点的用where，相当于相当于“介词+ which”，在句中做状语。

　　修饰原因的一般情况下跟的都是reason，用why关联词引导定语从句。

　　He came last night when I was going to bed.

　　I know of a place where we can have lunch.

　　She's going home where she can rest.

　　Do you know the reason why I left early?

　　There's no reason why he should do so.

　　4)非限定性定语从句 非限定性定语从句中不能用关联词that.修饰人时用who， whose， whom; 修饰物时用which， whose;修饰地点和时间的名词，且作状语时分别用where， when.如：

　　Water， which is a clear liquid， has many uses.

　　Our guide， who is a Chinese ， is an excellent cook.

　　They will fly to Boston， where they can plan to stay for four days， and then go to New York.

　　He picked up the book， the cover of which had been torn.(tear-tore-torn 撕裂、撕碎)

　　He is our English teacher， whose wife is a manager in a big firm.

　　非限定性定语从句还可以修饰整个句子，关联词只能用which.

　　The activity was postponed， which was exactly what we wanted.

　　They have invited me to attend the party， which is very kind of them.

　　限定型定语从句，如果修饰物并做宾语，前面又有介词，只能用which. 但是如果定语从句修饰的是不定代词，或是only，very以及形容词最高级，只能用that.在非限定性定语从句中修饰物只能用which，修饰人只能用who.如果非限定性定语从句修饰整个句子，关联词只能用which.