定语从句关系词选择依据先行词在从句中的成分来决定。
引导定语从句的关系代词有that,which,who（宾格whom），所有格whose）和关系副词 where when why 等，关系代词或关系副词在定语从句中充当一个成分，关系代词that，which,who,whom等在从句中分别作主语或宾语，whose在从句中作定语，而关系副词when,where,why等在从句中作状语。 如：
1.I will never forget the days when/in which we worked together.
我永远不会忘记我们一起工作的日子。
2.I will never forget the days which/that we spent together.
我永远不会忘记我们一起工作的日子。
解析：在句①中，表示时间的名词the days在从句中充当的是状语，所以用关系副词when来代指，引导定语从句修饰先行词the days；
而在句②中，表示时间的名词the days在从句中充当的是动词spent的宾语，所以用关系代词that或which来代指。
I saw a man shouting at a driver whose car was blocking the street.
我看见一个男人正朝一个司机叫嚷，他的车把街道堵塞了。
This is the little girl whose parents were killed in the great earthquake.这就是在那次大地震中失去双亲的那个小姑娘。
Mr Liu wants to talk to the students whose homework hasn't been handed in.刘老师要跟那些没交家庭作业的学生谈话。
whose为who的所有格，作“某(些)人的……”解，它所指代的先行词必须是人，其引导的定语从句修饰它的先行词，同时它本身在从句中作定语。
I saw some trees whose leaves were black with disease. 我看到一些树的叶子因病害而变黑。
The house whose windows are broken is empty. 窗户被打破的房子是空的。
The company whose name was Notco was in Australia.那个名叫诺特可的公司设在澳大利亚。
We live in a house whose windows open to the south.我们居住在一所窗户朝南开的房子里。
whose也可作which的所有格，作“某(些)物的……”解，它所指代的先行词必须是物，其语法功能同上。
whose既可引导限制性定语从句，亦可引导非限制性定语从句。
The boss in whose department Mr King worked called at the hospital.金先生工作单位的老板到医院来探视。(限制性定语从句)
小结：whose 是定语从句中一个常用的关系代词， 它是关系代词who的所有格，在从句中作定语，也就是说当先行词与从句中某个名词有所属关系，表达“……的”意思时，用关系代词whose 引导定语从句，它既可以指代人，也可以指代物，既可引导限制性定语从句，也可以引导非限制性定语从句。
同样，表示地点或原因的名词如果在从句中作状语，则用关系副词where 或why来代指；如果在从句中作动词的宾语，则用which或that来代替。 如：
1.This is the factory where/in which I worked.（作状语）
这是我工作的工厂。
2.This is the factory that/which I visited years ago.（作宾语）
这就是我几年前参观过的那家工厂。
注：当先行词为time,reason, place时，引导词可以省略。如：
This was the first time (when/what) I had serious trouble with my boss.
这是我第一次和老板发生严重的纠纷。
This is the first time(when/what) she has experienced disappointment
这是她第一次感受到失望。
It was the first time(when/what) I had put it all down on paper. I found it helped.
这是我第一次把所有的东西都写在纸上，我觉得这有帮助。
2.That is the reason (why) I did it. 这就是我做那件事的原因。
That is the reason ( why) the water of the sea is salty.
这就是为什么海水是咸的原因。
3.This is the place (where) we met yesterday. 这就是我们昨天见面的地方。
This is the place (where) the storm hit.
这就是暴风雨袭击的地方。
另外，定语从句中谓语动词的数应与先行词的数相一致。如：
1.Mr. Jackson is the only foreigner that is present at the party.
杰克逊先生是唯一出席晚会的外国人。
2.He is one of the students who were praised by the teacher.
他是受到老师表扬的学生之一。
解析：在句①中，先行词foreigner被only修饰，强调只有一个，所以从句中谓语动词用单数形式，而在句②中，who引导的定语从句修饰先行词the students，为复数，所以从句谓语动词应为复数。
