一、用法实例
“介词+关系代词+不定式”的表现形式通常为 in which to do sth, with which to do sth, on which to do sth等，其中的介词视具体语境的搭配而定。如：
She must have time in which to grow calm. 她需要有时间冷静下来。
She had no time left in which to pack her things. 她没有时间收拾行李了。
He had only the long nights in which to study. 他只有漫漫长夜可用来学习。
Allow me one minute in which to change my costumes. 给我一点时间来卸装。
Now he had no pretext on which to prolong his stay. 现在他已没有继续留下去借口。
He had a couple of revolvers with which to defend himself. 他只有一两把手枪用来自卫。
She had some money in the bank, with which to help her mother. 她银行里有些钱用来帮助她的母亲。
The boy wants another fifty cents with which to buy some ice cream. 这男孩还要五角钱去买冰淇淋。
It was a marvelous place to begin one's management career. First of all, there were so many different aspects of transport on which to try my hand. 这是开始一个人的经营管理生涯的好地方。首先，那里有涉及运输许多方面工作让我初试身手。
二、结构分析
在阅读中我们经常可以见到以上这样的“介词+关系代词+不定式”形式，许多读者不明白它是什么结构，其实它就是一种紧缩了的定语从句。在正式文体中，当引导定语从句的关系代词用作介词的宾语时，有时可用“介词+关系代词+不定式”这样的结构来简化定语从句。比较：
She must have time in which she can grow calm.=She must have time in which to grow calm. 她必须有冷静下来时的时间。
Allow me one minute in which I can change my clothes.=Allow me one minute in which to change my clothes. 给我一点时间换衣服。
He was miserable unless he had neighbors with whom he could quarrel.=He was miserable unless he had neighbors with whom to quarrel. 他要是没有邻居吵架就难受。
She had some money in the bank, with which she could help her mother. =She had some money in the bank, with which to help her mother. 她银行里有些钱用来帮助她的母亲。
三、补充说明
对于“介词+关系代词+不定式”结构，若语义清楚，且结构恰当，有时可进一步省略其中的关系代词，而只保留介词和不定式（注意，此时介词要移至不定式之后，且当先行词为表时间的名词时，该介词通常省略）。如：
She must have time to grow calm (in). 她必须有冷静下来时的时间。
Allow me one minute to change my clothes (in). 给我一点时间换衣服。
He was miserable unless he had neighbors to quarrel with. 他要是没有邻居吵架就难受。
It's reported that the city needs more land to build houses on. 据报道，这座城市需要更多的土地来建房。
四、特别提示
值得指出的是，“介词+关系代词+不定式”结构中的介词不能没有，并且该介词也不能位于不定式后面。如：
在那儿孩子们有个玩耍的花园。
正：There the children had a garden in which to play. (很正式)
正：There the children had a garden in which they could play. (较正式)
正：There the children had a garden to play in. (较口语化)
误：There the children had a garden which to play in.
