Ⅱ关系副词引出的定语从句
关系副词when指时间、where指地点，why指原因，她们引出的定语从句分别用来修饰表示时间、地点、原因的先行词如day, time, place, building, reason等。这些关系副词在从句中均做状语。例如：
e.g. In the days when black and white TV sets were so widely used, no one realized how soon color TV sets would replace them. 在黑白电视机如此广泛使用的日子里，没有人意识到彩电会那么快取代它。
e.g. How fast are we running now我们现在跑的速度怎么样? (多快)
e.g. How often do you go there 你多久去那里一次? (多久一次)
e.g. Ask him how he does it.问问他是怎样做的。
e.g. He does not know how to swim. 他不知道怎样游泳。
e.g. Air conditioning is very important in some industries where special conditions must be kept. 空气调节设备在一些需要保持特殊环境的工业部门十分重要。
e.g. Do you know the reason why things don’t fall off the earth?
你知道物体为什么不掉离地球的原因吗?
(fall off：下降，离开)

Ⅲ介词+which(whom)引出的定语从句
这种定语从句在修饰人时，介词后只用whom,修饰物时只用which,而不用that.例如：
e.g. The man with whom I share the room is a young teacher fresh from college.
与我同屋的人是一位刚从大学毕业的青年教师。
(fresh from school 刚由学校毕业)
e.g. This is the shelf on which I keep my books.这是我放书的架子。
e.g. The famous economist of whom we have often heard will come to give us a lecture next Friday.
我们常听说的那位经济学家下周五将给我们讲课。
(hear of: 听说 )
(give a lecture: 讲课，讲演 )
(attend a lecture 听报告;上课)
注：
当介词位于从句句末时，作为介词宾语的which和whom则仍可改用that,也可省略，如上面最后两句可改为;
This is the shelf (which或that)I keep my books on.
The famous economist(whom或that)we have often heard of will come to give us a lecture next Friday.

ⅠV.限制性(restrictive)定语从句和非限制性(non-restrictive)定语从句根据其与先行词的密切程度可分为限制性和非限制性定语从句。
1、 限制性定语从句
限制性定语从句与先行词关系密切，如去掉从句，句子的意思就不完整，不明确。从句与主句之间不用逗号隔开。译成汉语时，一般先译定从句，再译先行词，译成“…的…”.
2.非限制性定语从句
非限制性定语从句与先行词的关系比较松散,从句只对先行词附加说明,没有该从句句子的意思仍然完整。 主句与从句之间常用逗号隔开，翻译时一般分译成两个句子。所用关系代词与限制性定语从句基本相同，但that一般不用于非限制性定语从句。 如：
e.g. Mary has written several popular novels, one of which has been translated into ten foreign languages. 玛丽写了几本畅销小说, 其中的一本已经被翻译成十种外语. (which 指代several popular novels)
e.g.The professor introduced me to his students, most of whom were from abroad.
教授向我介绍了他的学生，其中大多数是来自国外。(whom指代his students)
e.g. They rowed across the Atlantic, which had never been done before.
他们划船横渡大西洋，这是史无前例的创举。(which指代前面整个句子的内容)
注：
非限制性定语从句除可修饰主句中的词外，有时还可修饰整个主句，这时所用的关系代词which代替的是整个主句或主句的一部分。从句中谓语动词用第三人称单数。如上面(3)个例句，which代替They rowed across the Atlantic整个主句。