如何判断定语从句中的引导词做什么成分

定语从句中关系副词的用法
关系副词,顾名思义,是联系先行词和定语从句的词,属于副词.定语从句中的关系副词有三个：when,where和why,它们在定语从句中分别作时间、地点和原因状语.其句法结构如下：
表时间的名词 + when + 定语从句
when指时间,在定语从句中作时间状语.
例句：I still remember the day when I first came to Beijing.
I’ll never forget the day when I joined the army.
表地点的名词 + where + 定语从句
where指地点,在定语从句中作地点状语.
例句：The factory where his father works is in the west of the city.
This is the house where I lived two years ago.
表原因的名词reason + why + 定语从句(why只用于reason之后的限制性定语从句中,在定语从句中作原因状语.)
例句：That is the reason why I did the job.(在现代英语中why可以省略)
上句也可以这样表示：
That is the reason I did the job.
又如：This was the reason (why )we raised the temperature.
关系副词在定语从句中的用法看似简单,以下注意点不可忽视：
1）“when”、“where”和“why”的运用取就于表时间的名词、表地点的名词和表原因的名词reason在定语从句中所作的成分,比较下面的几组句子：
*I will never forget the day when I first met you on the seashore.
*I will never forget the days which/that we spent together in Xueyao Middle School.
**This is the hospital where my mother works.
**This is the hospital which/that we visited the day before yesterday.
***The reason why he did not go to school is that he was ill.
***This is the reason which/that he gave his boss in the office .
2) “when”、“where”和“why”都可以替换成“介词 + which”,介词的选用取就于先行词和定语从句中的动词.例如：
Do you still remember the day on which we first met in Nantong?(on which=when)
This is the room in which we lived last year.(in which=where)
Do you know the reason for which he refused to go to Mary’s birthday party.(for which=why)
有时定语从句中介词短语和动词有意义紧密的修饰关系,尤其在非限制性定语从句中,常使用“介词 + which”结构,而不使用关系副词.例如：
My mother works in a factory,in front of which there is a small river.
At night the soldiers got to a small hill,at the foot of which stood a farmhouse.
3) 关系副词“when”、“where”既可引导限制性定语从句,也可引导非限制性定语从句.
例如：I will always remember the day when I first visited the Great Wall.
He came to Shanghai in 1980,when he was only 12.
I don’t know the exact spot where they will meet.
Mr Wang will fly to Beijing,where he will stay for three months.
有时关系副词“when”、“where”引导的限制性定语从句和先行词有间隔的现象,是为了平衡句子的语法需要.
Do you remember one afternoon ten years ago when I came to your house and borrowed a diamond necklace?
The days are gone forever when the Chinese people used “foreign oil.”.
4) “that”可活用为关系副词,相当于“when,where

如果引导词后有了主语（I ,we ,you,he,she等)就作宾语否则作主语