【从句讲解及练习】在英语语法中，从句是构成复杂句子的重要部分。从句不能独立成句，它必须依附于主句，并在句中充当一定的语法成分。常见的从句包括名词性从句、定语从句和状语从句等。以下是对这些从句的简要讲解，并附上练习题与答案。
一、从句分类及讲解
| 从句类型 | 定义 | 功能 | 举例 |
| 名词性从句 | 在句中起名词作用的从句，可以作主语、宾语、表语或同位语 | 作主语、宾语、表语、同位语 | I don't know what he wants.（宾语） |
| 定语从句 | 修饰先行词的从句，通常由关系代词或关系副词引导 | 修饰名词或代词 | The book that you gave me is very interesting.（修饰book） |
| 状语从句 | 表示时间、地点、原因、条件、目的、结果等的从句 | 修饰主句，表示各种逻辑关系 | I will call you when I arrive.（时间状语） |
二、常见从句用法总结
1. 名词性从句
- 主语从句：由 that / whether / if / what / who / when / where / why / how 引导。
- 例：What he said surprised everyone.
- 宾语从句：位于动词或介词之后。
- 例：She asked whether he was coming.
- 表语从句：位于系动词之后。
- 例：The problem is that we don’t have enough time.
- 同位语从句：解释说明前面的名词。
- 例：The fact that he failed made us sad.
2. 定语从句
- 关系代词：who / whom / that / which / whose
- 关系副词：when / where / why
- 限制性定语从句：不加逗号，对先行词起限定作用。
- 例：The man who is standing there is my teacher.
- 非限制性定语从句：用逗号隔开，对先行词进行补充说明。
- 例：My brother, who lives in Beijing, is a doctor.
3. 状语从句
- 时间状语从句：when / while / as / before / after / until / since
- 例：I will wait until you come back.
- 地点状语从句：where
- 例：This is where we met.
- 原因状语从句：because / since / as
- 例：He didn’t go because he was tired.
- 条件状语从句：if / unless / as long as
- 例：If it rains, we’ll stay at home.
- 目的状语从句：so that / in order that
- 例：She studied hard so that she could pass the exam.
- 结果状语从句：so...that / such...that
- 例：It was such a beautiful day that we went out.
三、练习题与答案
练习题：
1. I don’t know ______ he will come tomorrow.
2. The house ______ is on fire is my neighbor’s.
3. She left the room ______ she saw the accident.
4. He didn’t go to school ______ he was sick.
5. This is the place ______ we met for the first time.
答案：
| 题号 | 正确答案 | 解析 |
| 1 | whether / if | 宾语从句，表示“是否” |
| 2 | that | 定语从句，修饰house，关系代词that指代先行词 |
| 3 | when | 时间状语从句，表示“当……时” |
| 4 | because | 原因状语从句，表示“因为” |
| 5 | where | 地点状语从句，表示“在……的地方” |
通过以上讲解和练习，可以更好地掌握英语中从句的使用方法。建议多做相关练习，结合实际语境理解其用法。
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