定语从句子中介词加关系代词有三种情况。一种是根据先行词选择介词比如the day on which，另外两种情况是怎么样

用于这种情况的关系代词一般为which(指物)和whom(指人)。
在这种结构中，介词的选择非常关键，可以遵循以下四个原则：
(1)根据定语从句中的谓语动词确定介词，其动词与介词搭配，构成动词短语。
(2)根据定语从句中的形容词确定介词，其形容词与介词搭配，构成形容词短语。
(3)根据定语从句修饰的先行词确定介词，其先行词往往是表示时间、地点、原因、方法、工具等的词，它们与介词之间有一定的联系。当“介词＋关系代词”在定语从句中充当时间、地点、原因状语时，可分别用when, where,why替换。
(4)根据句子的意思确定介词。有些句子，先行词完全一样，定语从句中谓语动词不是由固定的动词短语构成的，这时，要根据句子所要表达的意思，选用不同的介词。如：
1. He was educated at a local grammarschool, _____ he went on to Cambridge.
A.from which B. after that C. after which D. from this
2. The schools themselves admit that not allchildren will be successful in the jobs ______ they are being trained.
A. inthat B. for that C. in which D. for which
3. I have many friends, some _____ arebusinessmen.
A. of them B. from which C.who of D. ofwhom
4. Mark was a student at this universityfrom 1999 to 2003, ______ he studied very hard and was made Chairman of theStudents’ Union.
A. during which time B. for which time
C. during whose time D. by that time
解析：第1题选C，after which 指“在此之后”；
第2题选D，考查的对应搭配是betrained for the jobs。
第3题选D，some of whom意为“其中有几个”。
第4题选A，“他学习努力并被选为学生会主席”应是“从1999至2003年这个期间里”所发生的事，所以用during which time。