深入讲解what、that、if等引导词的用法，轻松驾驭三类核心结构
一、什么是名词性从句？
名词性从句（Noun Clause）是一类在句中充当名词成分的从句，常用作主语、宾语或表语。由that, what, if/whether, who, how, why 等引导词引入。
二、三大类型解析
1. 主语从句
作用：在句中作主语，一般置于句首或句尾（句首常用形式主语 it 引导）。
结构形式：
- That she succeeded surprised everyone.
- It is clear that he made a mistake.
2. 宾语从句
作用：在动词、介词、形容词后作宾语，是学生接触最早、使用最广的名词性从句。
常见结构：
- I know that he is right.
- She asked if you were coming.
- Do you know what he wants?
**注意：**陈述句变宾语从句，语序不变，时态一致；疑问句变宾语从句，语序恢复正常。
3. 表语从句
作用：位于系动词（如 be, seem, look 等）之后作表语，说明主语的性质或状态。
示例：
- The fact is that we are late.
- The question is whether she will come.
三、引导词用法对比
| 引导词 | 用途 | 示例 |
|---|---|---|
| that | 引导陈述性内容 | I believe that she is honest. |
| if/whether | 引导选择性内容 | I wonder if she will come. |
| what | 引导“什么” | I don’t know what she said. |
| who/whom | 引导“谁” | I don’t know who he is. |
| how/why/when | 引导方式、原因、时间 | Tell me how you did it. |
四、写作范文片段
What he said at the meeting surprised all of us.
Most people believe that success depends not only on hard work, but also on strategy.
The truth is that we didn’t prepare enough.
这些句子在写作中能有效丰富表达层次，增强逻辑清晰度，是中考、高考及四六级作文常用结构。
五、常见易错点提醒
- ❌ I don’t know what does he mean.
✅ I don’t know what he means.
（宾语从句中要用陈述语序） - ❌ She asked does he like it.
✅ She asked if he liked it.
六、结构训练建议
- 写 5 个含主语从句的句子
- 写 5 个宾语从句转换题（由陈述句改为宾语从句）
- 观察新闻标题或演讲稿中表语从句的运用方式
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