有这样一道考题：

It’s reported that the city needs more land _____.

A. on which to build houses            B. on which building houses

C. which to build houses                 D. which to build houses on

此题答案为A，许多同学不明白此句是什么结构。简单地说，这是一个紧缩了的定语从句，这类结构可归纳为“介词+关系代词+不定式”形式。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。如：

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。

若语义清楚，且结构恰当，“介词+关系代词+不定式”有时可进一步将其中的关系代词省略，而只保留介词和不定式(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。

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.

（编辑  陈根花）