1)当先行词是all,anything,everything,something,nothing等不定代词或先行词前有first,last,any,few,much,some,no,only以及形容词最高级修饰时，只能用关系代词that引导从句。如：
That is all that I've heard from him.He's the first person that I'm going to interview this afternoon.
2)关系代词的省略在从句中作宾语的关系代词常可省略。关系代词紧跟介词，作介词宾语时不可用that，只可用which或whom引导从句，并且不可省略，但当介词位于宾语从句句末时，作为介词宾语的关系代词仍可用that，也可省略。如：This is one of those things with which we have to put up.This is one of those things (which\that) we have to put up with.
3)引导定语从句的关系副词有when,where,why等。关系副词在从句中作状语，意义上相当于一个“介词+which”的结构。如：Even in comic books where(=in which) there are no words,the stories are fully expressed through the drawings.No one knows the reason why(=for which) he was so angry that day.
*→非限制性定语从句非限制性定语从句既可修饰先行词，也可修饰整个主句，起补充说明作用，与主句之间有逗号隔开，若省去，原句意思不受影响。不可用that引导非限制性定语从句。关系词不可省略。如：Every object has a gravitational pull,which is rather like magnetism.
*“介词+which\whom\whose”引导的定语从句“介词+which\whom\whose”可引导限制性定语从句，也可引导非限制性定语从句，该结构中介词的选择取决于从句谓语动词的固定搭配，或先行词的习惯搭配。如：This is the computer on which he spent all his savings.It is written by a person with whom we are all familiar.
*as引导的定语从句as引导的定语从句主要用于“such...as”及“the same...as”的结构中，代替先行词是人或物的名词。as引导非限制性定语从句时，代替整个主句，从句可位于主句之前、之后或中间。如：These are not such problems as can be easily solved.(as代替先行词problems)As is mentioned above,no single company or group can control what happens on the Internet.(as代替主语)
2.状语从句→时间状语从句引导时间状语从句的从属连词和词组有：1）when,whenever,while,as,after,before,since,till,until,once等。We have learnt quite a lot about it since we came here.2)as soon as,hardly(scarcely)...when,no sooner...than,each(every) time,the moment,immediately(that)等。As soon as I sent an e-mail message,I received positive responses.The moment he heard the good news,he jumped with joy.
→地点状语从句引导地点状语从句的连词是where,wherever.Wherever she went,she took her little daughter with her.
→原因、结果和目的状语从句1）引导原因状语从句的从属连词有：because,as,since,now(that),seeing that,considering that,in that等。Considering that he is a freshman,we must say he is doing well.2)引导结果状语从句的连词有：so...that,such...that,so that,that,so等。Mickey Mouse is so attractive that the children are reluctant to leave.3)引导目的状语从句的连词有：so that,in order that,for fear that,lest等，从句常使用may,might,can,could,would等情态动词。We got up early this morning so that we could catch the first bus to the railway station.
→条件和让步状语从句1）引导条件状语从句的连词和词组有if,unless,as(so) long as,on condition that,in case,provided(providing) that,supposing等。As long as you have the right equipment,you can use a telephone line to transmit computer data.2)引导让步状语从句的连词和词组有though,although,whether,even though,even if,no matter what(when,how...),whatever(whenever,wherever,however....)等。though,even if等引导状语从句可转换成含有as的部分倒装结构，具有强调意义。其结构为“形容词（副词、动词、名词）+as+主语+谓语”。No matter what you may say,I would not change my mind.Young as he is,he is quite experienced in this work.(=though he is young)Child as he is,he can speak English fluently.(=though he is a child)
→方式状语从句引导方式状语从句的连词有as,just as,as if,as though等。as if,as though引导的状语从句中，谓语动词常用虚拟语气，表示与事实相反。The young man made the experiment just as the teacher had taught him.Everything went on as usual as if nothing had happened.
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