定语从句的引导词分为关系代词(who， whom， whose， which， that)和关系副词(where， when， why)两类，这些引导词在引导定语从句的同时均在从句中充当成分。关系代词可作主语、宾语和定语，作宾语时可省略;关系副词可作状语，一般不能省略。下面简单介绍一下定语从句的难点。
一、介词(短语) + 关系代词 / 副词
1. 此处关系代词只能是which / whom / whose / where / when，而不能用who / that.
如：They arrived at an old building， in front of which stood a tower. He climbed up to the top of the tree， from where he could see clearly what was happening in the woods.
2. 不定代词 / 数词 + of which / whom.
如：Mrs. Green has three sons， none of whom works in the city. The boys discovered many pictures on the walls of the cave， most of which dated back to 15，000 years ago.比较：The boys discovered many pictures on the walls of the cave， most of them dating back to 15，000 years ago. (此处是独立主格结构)
指物时whose + 名词 = of which + the + 名词 / the +名词 + of which.
如：The plastic bottle， whose top / of which the top / the top of which is cut off， can be used as a container to grow plants in.比较：The plastic bottle， (with) the top cut off， can be used as a container to grow plants in. (此处为独立主格结构)
用来指代整个主句的内容， which 引导的从句只能放在主句后，as 引导的从句放在主句前后均可;which 意为“这一点”，as 意为“正如”。as还可用于the same …… as， such …… as等结构中，引导限制性定语从句。
如：He turned out to be a great success as a dancer， which was more than we could expect. As is known to all， Madame Curie is the first woman scientist in the world to have won two Nobel Prizes. Have you bought the same dictionary as I referred to yesterday?
用where 引导定语从句的特例通常先行词是地点名词，且定语从句的引导词在从句中作地点状语时，用where 引导定语从句，但有时先行词是非地点名词时，也须用where 引导定语从句，表示抽象意义的一种状态，此类词包括point， situation， case 等。
如：The treatment will continue till the patient reach the point where he can walk correctly and safely. (point意为“程度”)
Can you think of a situation where this idiom can be used? (situation意为“情景”)
There‘re always cases where non?鄄native English speakers can’t make themselves understood just because of their lack of culture background of the visited countries. (case意为“情形，情况”)
1. way作先行词，意为“方式、方法”时，引导词在从句中作状语，可用that / in which 引导，也可省略;若引导词作从句的主语或宾语，用that / which 引导，引导词作宾语时可省略。
如：I‘ve thought of a good way (that / in which) we can conduct the experiment successfully. The way that / which will be used to carry out the operation was suggested by Doctor White. This is the very way (that / which) we need to test the theory.
2. 先行词是time时，若表示“次数”，应用that引导定语从句，that可省略;若time表示“一段时间”，则用when或at / during + which引导定语从句。
如：This is the second time (that) the President has visited the country. This was at a time when / during which there were no radios， no telephones or TV sets.