知识点4：why的用法：

why表示原因，在定语从句中作原因状语，其先行词一般为reason。

The reason why she told a lie is unknown. 她为什么撒谎还不清楚。

知识点5：.“介词＋关系代词”的用法 1.【考查点】用法

关系代词whom，which在定语从句中作介词的宾语时，可以跟介词一起放在主句和从句之间；为了使关系代词紧跟它所修饰的先行词，也可以把介词放在从句中有关动词的后面。 This is the room in which we lived last year. ＝This is the room which we lived in last year.

2.【考查点】注意事项

定语从句中“介词＋关系代词”结构中的关系代词是which(指物)，whom(指人)。掌握这个结构的关键在于对介词的正确选择，要注意以下几个问题：

(1)介词与定语从句中的动词是一种习惯性搭配。 This is the room in which we lived last year. ＝This is the room which we lived in last year. 这就是我们去年住过的房间。

(2) 介词与定语从句中的形容词一起构成一种习惯性搭配。

The two things about which Marx was not sure were the grammar and some of the idioms of English. ＝The two things which Marx was not sure about were the grammar and some of the idioms of English.

马克思在语法和英语的某些习惯用语这两方面还是没有把握。