Why的用法

一、why 作“为什么”、“为何”讲

1. Why is X equal to Y? 为什么 X 等于 Y？
2. Why did he do that experiment once and again? 为什么他再三地做那个实验？

二、why 引导各种从句

1. She knows why certain elements are very much alike in properties. 她知道为什么某些元素在性质方面十分相象。（宾语从句）
2. Do you know the reason why there are heat losses in a steam engine? 你知道为什么蒸汽机内有热损耗吗?（句中 why 为关系副词，引出定语从句。）
3. It is clear now why heat can be produced by friction. 现在很清楚，为什么摩擦能产生热。（主语从句）
4. The question is why metals are good conductors. 问题是为什么金属是良导体。（表语从句）
5. Please answer the question of why acids eat in (或 eat away) metals. 请回答为什么酸腐蚀金属的问题。（介词 of 的宾语从句，连同 of 修饰 question。）
6. He has solved the question (of) why resistance is affected by temperature. 他解决了为什么温度影响电阻那个问题。（同位语从句）

三、注意在一定上下文中，why 后只用不带 to 的不定式动词或其短语

1. Why get so excited？为什么如此激动？
2. Why not go together with him？为何不和他一起去呢？
3. Oh，you look weak today. Why you not go and see the doctor？奥，你今天脸色显得虚弱。为什么不去看医生？（第二部分也可改为：Why didn't you go and see the doctor？）
4. Why haven't you sent him away? 为什么还没有打发他走？
5. Why did you become a chemistry teacher? 为何你当了一名化学教师？
6. Why let her come in? She well stand in the way. 为什么让她进来？她会碍事的。（第一部分有 Don't let her come in 含义。）
7. We should praise the girl for the reason why she studies best. 我们应该表扬这位女孩，因为她学习最好。(for the reason why 或 for the reason that 均可引出原因状语从句。）