从关系词用法到句型变形，全面吃透定语从句结构与用法
一、什么是定语从句？
定语从句是用来修饰名词或代词的从句，整个从句起到定语的作用。它通常紧跟在被修饰词之后，连接词叫做关系词（包括关系代词和关系副词）。
二、关系词分类与功能
1. 关系代词：who, whom, whose, which, that
| 关系代词 | 指代对象 | 在从句中作 | 示例 |
|---|---|---|---|
| who | 人 | 主语 | The boy who is running is my brother. |
| whom | 人 | 宾语 | The man whom you met is my teacher. |
| whose | 人/物 | 定语 | The girl whose bike was stolen is crying. |
| which | 物/动物 | 主语/宾语 | The book which is on the desk is mine. |
| that | 人/物 | 主/宾 | The movie that we watched was great. |
2. 关系副词：when, where, why
| 关系副词 | 指代内容 | 示例 |
|---|---|---|
| when | 时间 | I remember the day when we first met. |
| where | 地点 | This is the house where I was born. |
| why | 原因（常搭配reason） | That’s the reason why he left. |
三、限定性与非限定性定语从句
✅ 限定性定语从句（Essential）
提供关键信息，不加逗号，不能省略：
- Students who study hard usually perform better.
- The car that broke down belongs to Tom.
✅ 非限定性定语从句（Non-essential）
补充说明，用逗号隔开，不能用 that 引导：
- My father, who is a teacher, loves literature.
- This book, which was published in 1995, is out of print.
四、易错点提醒
- 非限定性从句不能用 that：
❌ My car, that is blue, is fast.
✅ My car, which is blue, is fast. - 主语重复错误：
❌ The girl who she met us yesterday is my cousin.
✅ The girl who met us yesterday is my cousin. - 混用关系词：
不要随便用 which 代替 who 或 vice versa。
五、句型变换练习
将两个句子合并为定语从句：
- She is the teacher. She taught me French.
✅ She is the teacher who taught me French. - This is the school. I studied here for three years.
✅ This is the school where I studied for three years.
六、写作范文片段（适合中考或高一英语作文）
There are many students who work very hard every day, but not all of them get good grades. A student who studies with the right method can often achieve better results than those who just spend time. That’s the reason why we should learn to study wisely.
✔️ 本段运用了4个定语从句，分别修饰 people、students、those 和 reason，句式自然，逻辑清晰。
七、学习建议：
- 练习合并简单句为定语从句；
- 注意逗号使用与关系词搭配；
- 多模仿例句，写出自己的定语从句句式。
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