介词+关系代词
“介词+关系代词”引导的定语从句普遍用于正式的文体中，在非正式文体中介词也能够放在后面，比如I found a room in which I can study.(正式) = I found a room I can study in.(非正式) 。
“介词+关系代词”的情况一般用来替代关系副词(where，when，why)，when和where都能够用in/on/at which来替代，而关系副词why被for which取代时有一个条件，即前面的先行词必须是the reason。
能够用“介词+关系代词”这种形式的关系代词主要有which和whom，个别情况有whose。判断是否用“介词+关系代词”一般有这样两个依据：
1. 根据从句中的动词，形容词，名词和介词的固定搭配而定。
2. 根据先行词与从句中动词的关系及其含义而定。
让我们从新概念三册的原句中来学习一下
第5课： However, he had at last been allowed to send a fax in which he informed the editor that…… (in which中的which代指的是fax，而在传真中应该是in
the fax)
第17课： Verrazano, an Italian about whom little is known, sailed into New York Harbour in 1524 and named it Angouleme. (这里牵扯到固定用法：know about，表示对…有所了解)
第17课： They support the cables from which the bridge has been suspended.(这里是和后面动词的固定搭配相关，be suspended from)
第32课： The most valuable find of all was the ship's log book, parts of which it was still possible to read. (which表示log book，这里作者要表达的是log book 的一部分，所以用part of)
第60课： She felt inhere handbag for the piece of paper on which her father had written down all the details… … (这里如同第5课的原句，介词搭配和名词paper相关，应该是on the paper)
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