where : 当先行名词在从句中当地点状语时，用关系副词where连接
例如：
The crime rate rises in cities where the unemployment rate increases. 句中的where = in cities, 表示行为发生的地点。
这里的要点是能否区分是用that 还是用 where， 即：是做主语、宾表语，还是做地点状语，例如：
I love the small town that we visited last week.
句中town做动词visited的宾语，即参观过的小镇，故用that连接。
I love the small town where I lived during my childhood.
句中town 是动词lived的地点，即童年时住过的小镇，故用where.
这也是定语从句的一个考点。
when : 当先行名词在从句中当时间状语时，用关系副词when连接, 例如：
July is the month when we have a lot of rain.
注意when定语从句后推的现象，例如：
I think the day will finally come when air pollution can be put under control.
放在主句后面作非限制定语从句时，when一般译为此时，那时, 例如：
The meeting will be put off until next month, when we will have made all the preparations.
另一个关系副词是why，由于它固定与the reason搭配, 即： the reason why，不难理解，一般也不作为考试的重点。例如：
This is the reason why the electronic computer cannot entirely replace man. 这就是电子计算机不能完全代替人的原因。
whose ：做先行词的定语，汉语为的，不要考虑是否是限制性或非限制性定语从句, 例如：
Pay attention to that boy whose temperature is very high. / 注意那个体温很高的男孩。
介词 + which
先看两个句子：
This is the house. He has lived in the house for over 30 years.
变为定语从句
This is the house in which he has lived for over 30 years.
上述句子中，先行词在从句中充当介词宾语，形成介词 + which / whom的形式，考试时要求作出1)要不要介词;2)若要，使用什么介词的判断。由于英语中介词搭配多为习惯用法，没有多少规律可循，因此这是定语从句考试的一个难点。
记住四个字：瞻前顾后
瞻前：先看看先行词一般与什么介词搭配，例如：
There are occasions _____ which joking is not permissible.
Joking is not permissible _____ occasions.
常与occasion搭配的介词是什么?on， 即：
Joking is not permissible on occasions.
There are occasions on which joking is not permissible.
顾后：看看谓语动词常与什么介词搭配，例如：
This car, ____ which I paid a lot of money, is now out of date.
I paid a lot of money ______ this car.
Pay for something 是一个固定的搭配，因此应填介词 for
当A、B、C、D中出现 介词 + which / whom 选项时，而你又确实看不懂时，应倾向于选择 介词 + which / whom的形式，例如：
The two elements _____ water is made are the gases oxygen and hydrogen.
A. that
B. which
C. with which
D. of which
倾向选择C、D;正确答案D，be made of :
The two elements are gases .
Water is made of the two elements.
两个句子一合并，便是该句选择。
其他应注意的确问题：
同位语从句只能用that连接
常见的同位语先行词有：fact, possibility, idea, belief, doubt, news, order, promise, evidence, suggestion等，例如：
Is there any possibility that all the villagers can send their children to school?
There can be no doubt that he is a qualified doctor.
as 也可以做关系代词用于连接定语从句，特别是在suchas, the same as 以及正如的结构中，例如：
I have never seen a thing as he described.
As was expected, the performance was a great success.
把该句理解为：The performance was a great success, which was expected，就比较容易理解as的这种用法。
将定语从句的连接用三句话归纳一下：
↗ 人用who / whom
先行词在从句中当主、宾、表语 定语用whose
↘ 物用that / 非限制用which
↗地点状语用：where
先行词在从句中当 原因状语用：why
↘ 时间状语用：when
介词 + which / whom结构：瞻前顾后