肯定句转疑问句
在英语里，把肯定句变成一般疑问句（yes/no question），通常是把句中的“助动词/情态动词/系动词”提前到主语前面；如果原句没有助动词，则用 do‑support（在一般现在时和一般过去时中引入 do/does 或 did）。下面分几种情况说明，并以 “They have three pets.” 为例。
1. 有助动词（包括情态动词 can, must, will…）或 be 动词
结构：助动词/系动词 + 主语 + 其它成分 + ？
示例：
- They are happy. → Are they happy?
- She can swim. → Can she swim?
- He has been there. → Has he been there?
注意：这里的 “has” 是完成时的助动词，所以直接提到句首。
2. “have” 作实义动词（表示“拥有”）
结构：Do/Does + 主语 + have + … + ？
示例：
They have three pets.
- 一般疑问句：Do they have three pets?
- （在口语中，也用 “Do they have…?”，没有缩写。）
She has a car. → Does she have a car?
主语是第三人称单数用 does，其他人称用 do。
3. 一般现在时／一般过去时（主要动词）
结构：Do/Does/Did + 主语 + 动词原形 + … + ？
示例：
- You play basketball every week. → Do you play basketball every week?
- He went there yesterday. → Did he go there yesterday?
过去式都用 did，动词用原形。
4. 完成时（have + 过去分词）
结构：Have/Has + 主语 + 过去分词 + … + ？
示例：
- I have seen that movie. → Have you seen that movie?
- She has finished her homework. → Has she finished her homework?
5. 进行时（be + –ing）
结构：Am/Is/Are + 主语 + 动词‑ing + … + ？
示例：
- They are watching TV now. → Are they watching TV now?
- I am reading a book. → Am I reading a book?
6. 带其他情态或复合结构
如果句子中有多个助动词，顶层的助动词放句首：
- She will be here soon. → Will she be here soon?
- They should have told us. → Should they have told us?
小结
- 有助动词：直接把最前面的助动词（包括 be、情态、完成时的 have）提到主语前。
- 没有助动词：一般时态下用 do‑support——用 do/does/did + 主语 + 动词原形。
- 注意时态一致：助动词形式要与原句时态和主语人称一致。