【什么情况下用do和does】在英语语法中，"do" 和 "does" 是助动词，常用于构成一般现在时的疑问句和否定句。它们的使用取决于主语的人称和数。正确使用 "do" 和 "does" 是学习英语的基础之一，尤其对初学者来说尤为重要。
一、基本规则总结
1. 当主语是 I, you, we, they 时，使用 do。
2. 当主语是 he, she, it 时，使用 does。
3. do 和 does 的作用是帮助构成疑问句和否定句。
4. 在肯定句中，不需要使用 do 或 does。
二、常见用法对比表
| 主语 | 肯定句（肯定形式） | 否定句（否定形式） | 疑问句（疑问形式） |
| I | I go to school. | I do not go to school. | Do I go to school? |
| You | You go to school. | You do not go to school. | Do you go to school? |
| We | We go to school. | We do not go to school. | Do we go to school? |
| They | They go to school. | They do not go to school. | Do they go to school? |
| He | He goes to school. | He does not go to school. | Does he go to school? |
| She | She goes to school. | She does not go to school. | Does she go to school? |
| It | It goes to school. | It does not go to school. | Does it go to school? |
三、使用小贴士
- 在疑问句中，do/does 放在主语前面。
- 在否定句中，not 跟在 do/does 后面。
- 当句子中有实义动词时，do/does 必须出现。
- 如果没有实义动词，如 “He is a student.” 这类句子，就不需要使用 do 或 does。
四、常见错误示例
| 错误句子 | 正确句子 | 原因 |
| Do he go to school? | Does he go to school? | 主语是 he，应使用 does。 |
| She don't like apples. | She doesn't like apples. | 主语是 she，应使用 doesn't。 |
| We does not go. | We do not go. | 主语是 we，应使用 do。 |
通过掌握这些规则，你可以更准确地使用 "do" 和 "does" 来构造正确的英语句子。建议多做练习，特别是在实际对话和写作中不断运用，以加深理解和记忆。
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