一、用法说明
介词+whom只能指人；介词+ which只能指物。如：
Look, there comes Tom, for whom I have waiting for an hour. 瞧，汤姆来啦，我等他等了一个小时。
Last Saturday evening, I went to Wu Dong’s birthday party, in which I met a foreigner named Jim. 上周星期六的晚上我去参加了吴东的生日聚会，在会上我会到了一个叫吉姆的外国人。
She came into the house, on whose wall there was a portrait of Einstein. 她进入了房间，房子的墙壁上有一张爱因斯坦的画像。
二、注意事项
(1) 有时，前面的介词可移到定语从句的中间或后面，此时whom可用who, that代替；which可以用that代替。而且who, whom, which, that都可省略。如：
The man with whom you talked just now is our manager. —The man who you talked with just now is our manager. 你刚才与他谈话的那个人就是我们的经理。
He handed me a pen, with which I wrote down my address for him. —He handed me a pen, which I wrote down my address with for him. 他递给我一支钢笔，我就用那支钢笔给他写下了我的地址。
(2) 当先行词是时间、地点、原因从句时，介词+ which一般在定语从句中分别做时间、地点、原因状语，于是介词+ which可以分别用when, where, why代替。但若介词+ which不是作时间、地点、原因状语，则不能用when, where, why代替。如：
Last week, I visited Shanghai, in which I have made several friends. —Last week, I visited Shanghai, where I have made several friends. 上周我参观了上海，在那儿我叫上几个朋友。
I will remember the day forever on which I won the first place in the contest. —I will remember the day forever when I won the first place in the contest. 我将永远记住我在竞赛中获得第一名的那一天。
三、介词的选用
介词+关系代词引导定语从句时，介词往往受上下文的约束，究竟使用哪个介词时得从下面几方面来进行考虑。
(1) 从先行词跟介词的搭配习惯出发。如：
In front of my house, there is a tree, in which some birds are singing. 我的房子前有一棵树，鸟儿正在树上唱歌。(在树上一般用介词in)
(2) 从定语从句中的动词、形容词对介词的习惯要求出发。如：(from www.yygrammar.com)
The computer for which I paid 5,000yuan is made in Shenzhen. 我花了五千元所买的这台电脑使深圳造的。( pay 与for搭配)
(3) 从先行词、定语从句中的动词或形容词两方面同时考虑出发。如：
Do you know the girl with whom the man talked just now? 你认识跟那个男谈话的女孩吗？(talk 究竟接to, with还是接about, 这该由动词及现行词一起决定)
(4) 复合介词+关系代词。如：
Go down this road, at the end of which you can see a high building and it is our office building. 沿着条路走，在路的尽头你会看到一座高大的建筑，那就是我们的办公大楼。
(5) 名词+介词+ 关系代词。如：
He has three children, one of whose children is studying abroad now. 他又三个小孩，其中一个在国外读书。
注意：当定语从句的动词与介词是不可分割的固定搭配时，介词不能放到关系代词之前。如：
She has a little daughter, who is looked after by her grandma. 就不能写成：She has a little daughter, after whom is looked by her grandma. 因为，look after 是不可分开的固定短语。
网页链接
感觉这个网站讲得已经挺清楚的了，就直接摘抄了，有疑问可以继续提。
介宾短语就是介词接作宾语的名词，它在句子中通常是作为状语的副词短语。
The students learn lessons at the class.
at the class就是介词at接名词the class形成的介宾结构作为一个副词短语充当句子中的状语。
This is the class where the students learn lessons.
上面引导定语从句的是一个关系副词where，它代替了从句中的整个状语at the class.
This is the class which the students learn lessons at.
这里引导从句的是关系代词which，他代替的是从句中作状语的介宾结构中的宾语，也就是名词the class。
当引导从句的是关系代词，用来代替作状语的介宾短语中的宾语时，介宾短语中的介词可调到关系代词前，形成介词加关系代词引导从句的情况。
This is the class at which the students learn lessons.
再举一些简单的例子：
The public toilet where/to which he went is very clean.（He went to a public toilet，which is very clean）
where代指to the public toilet，which代指the public toilet。
It was 19th century when/in which i had not benn born.（i was not born in 19th century）
when代指in 19th century，which代指19th century。
烽火连三月，家书抵万金。
内容全部来源于网络收集，如有侵权，请联系网站删除：QQ：24596024