定语从句纲要：
（这是相关定语从句的精要绍介，包括了相关定语从句的多种方面，供参照：）
指导定语从句的关涉词涵盖关系代词和关系副词。关系代词有that, which, whose, who, whom, as；关系副词有when, where, why。关系代词和关系副词在定语从句中都担任一定的句法成份。关系代词在从句中高一英语语法担任动词的宾语时普通可以省略。
关系代词的选用比较复杂，受下面所开列条件的抑制：
(1) 要看先行词是指人或者指物，
(2) 要看关系代词在从句中句法功能，
(3) 要看定语从句是框定性的或者非框定性的。
在定语从句中担任的成分
↓ 用于框定性或非框定性从句 只用于框定性从句
指人 指物 指人或指物
主语 who which that
宾语 whom which that
谓语 whose whose (of which)
That 只能用在框高一英语语法定性定语从句中，而who, whom, which, which 既可用于框定性定语从句中，也可用于非框定性定语从句。
I know that he is a man who means what he says.
I know that he is a man that means what he says. 【我晓得他是一个守信誉的人。】
The gentleman whom she met addressed her with courtesy.
The gentleman that she met addressed her with courtesy. 【她碰到的那位先生很有礼貌地向她打了招呼。】
The gentleman she met addressed her with courtesy.（在从高中英语语法定语从句
句中担任动词宾语的关系代词，可以省略。）
The watch which was lost has been found.
The watch that was lost has been found. 【丢了的表找到达。】
Here is the material which you need. (注：现代美语中不准许这么用)
Here is the material that you need.
Here is the material you need. 【你要的材料在这儿了。】
You are the only one whose advice he might listen to. 他也就是听你的话吧。
关系副词的选用相对高一英语语法来说比较简单，假如先行词是表达时间的表名称的词，如time, day 等，则用when, 如先行词为表达地点的表名称的词，如place, house, area 等等，则选用where。假如先行词为reason 则选用why
I will never forget the mountain village where I spent my childhood.
I will never forget the mountain village in which I spent my childhood.
我永恒也不会遗忘我度过幼年的那一个山包村。
I don’t know the reason why he did that.
I don’t know the reason for which he did that. 【我不晓得他为何这样做。】
当先行词是all, something, nothing 等不稳定代词时，还是先行词的面前有first, last, only, few, much, some, any, no 等词修饰时，还是先行词的面前有顶级修饰时，普通只用that 而无须which 来指导定语从句：
I have explained everything that I can to you.
I have explained everything I can to you. 【我已经尽一切有可能把事物向你诠释得一清二楚。】
This is the most beautiful campus that I have ever been to.
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