1,在介词后只有which,不用that，如I like the house around which there are plenty of trees;
2,既代人又代物的，用that,不用which;
3,被修饰词前有every,only,any,some,almost,nearly等词时，只用that。
   
定语从句的关系词有很多，而且用法也很复杂，下面将几个关系词的"使用权限"进行归纳以使同学们掌握学习。 　　一、只能用that,不能用which, who 的几种情况: 　　1。先行词是人和物 　　The person and his dog that were killed in the accident were buried。
   　　The man and his school that you told me are very interesting。 　　2。先行词是不定代词anything, something, everything, nothing, all, the one 等 　　Has everything that can be done been done? 　　All that you told me was difficult to understand。
   　　3。先行词被最高级修饰 　　It is the longest film that I have seen in my life。 　　4。先行词被序数词修饰 　　It's the first time that I've been to Beijing。
   　　The first stamp that was invented appeared in England。 　　5。先行词被just ,very, only等强调词语所修饰 　　It's the very house that I want to buy。
   　　Only the vegetables that haven't been polluted are safe to eat。 　　二、只能用which, who,不能用that的两种情况: 　　1。非限制性定语从句 　　The Changjiang River, which is the third longest river in the world, lies in China。
   　　Do you know Tom, who used to be the headmaster of this school? 　　2。整句话当先行词 　　It rained a lot, which made a flood happen。
   　　He tore my photo, whichmademeangry。三、只能用as,不能用which,that,who的两种情况:1。先行词被such,thesame修饰I'veneverheardofsuchaterribleearthquakeasyoutoldme。
  对比:It'ssuchaterribleearthquakethatmanypeoplewerekilled。分析:定语从句的动词和先行词有动宾关系,如上面第一句应用as;结果状语从句应用such。。。that句型,表示"如此……以至于",如上面第二句。
  2。整句话当先行词,且从句有"正如……所知道/预料的一样"之意TaiwanbelongstoChina,asweknow。Aseverybodycansee,wehaveagoodharvestinfruitthisyear, 与which以整句话当先行词的区别:1。
  which引导的句子有"这就使……"造成某些客观后果的意思,而as引导的句子都含有主观认识的动词:如know,see,expect之类。 引导的定语从句可放在句首,这是唯一能放在先行词前的定语从句。当然,它也可放在先行词后。而which却只能放在先行词后,不能放在句首。
  四、that,which,who等关系代词在作定语从句中的宾语时可省略。如:Thisisthehouse(that/which)mygrandparentsbuilttwentyyearsago。Theperson(who/whom/that)youjustspoketoisourheadmaster。
  五、只能用when,where,不能用that,which的情况:关系代词在从句中作状语。例如作live,work,study等不及物动词的状语。试比较:I'llneverforgetthedaysthatwespenttogether。I'llneverforgetthedayswhenwestudiedtogether。
   　　He enjoyed the place that/ which he visited a week ago in Wuhan。 　　He enjoyed the place where he stayed a week ago in Wuhan。
  
1,在介词后只有which,不用that，如I like the house around which there are plenty of trees;
2,既代人又代物的，用that,不用which;
3,被修饰词前有every,only,any,some,almost,nearly等词时，只用that。