范文：
标题：must的过去式
正文：
在英语中，"must" 是一个情态动词，用来表达必要性、命令或推测。它的过去式通常使用 "had to"。以下是一些关于 "must" 的过去式的用法示例：
1. 表达过去的必要性：
We had to leave early because the train was late.
He had to finish his work before going on vacation.
2. 表示过去的命令：
You had to be quiet in the library.
She had to follow the rules strictly.
3. 表达过去的推测或义务：
I thought he had to be at the meeting, but he wasn't there.
You had to clean your room before you could go out.
"Must" 的过去式 "had to" 在句子中通常作为实义动词使用，可以构成进行时或完成时态，如下所示：
We were had to wait for hours because of the traffic.
They had finished their homework before they went to bed.
总结来说，"had to" 是 "must" 的过去式，用于描述过去某种情况下的必要或被迫去做某事。
常见问答知识清单及解答：
1. 问题：什么是 "must" 的过去式？
解答："must" 的过去式是 "had to"，用于表示过去的必要性、命令或推测。
2. 问题："had to" 和 "had to do" 有区别吗？
解答：没有区别。"had to" 和 "had to do" 都可以用来表示过去必须做某事。
3. 问题：什么时候用 "had to"？
解答："had to" 用来表示在过去某段时间内，由于某些原因不得不做某事。
4. 问题："had to" 能构成进行时吗？
解答：可以。例如："They were having to wait for the bus."
5. 问题："had to" 能构成完成时吗？
解答：可以。例如："He had to finish the project before the deadline."
6. 问题："must" 的过去式可以和 "do" 搭配吗？
解答：不可以。"must" 的过去式是 "had to"，而不是 "had to do"。
7. 问题："must" 的过去式可以用于疑问句吗？
解答：可以。例如："Did you have to go to the store yesterday?"
8. 问题："must" 的过去式可以用于否定句吗？
解答：可以。例如："I didn't have to finish my homework yesterday."
9. 问题："had to" 和 "needed to" 有什么区别？
解答："Needed to" 更强调需要或有必要做某事，而 "had to" 则强调被迫或不得不做某事。
10. 问题："had to" 能用于虚拟语气吗？
解答：可以。例如："I wish I hadn't had to leave so early."（我希望我没有那么早离开。）
