动词不定式是英语语法中非常重要的非谓语动词形式，八年级学生需掌握其核心用法。以下是七种常用用法及示例：

一、作主语

基本结构：

It + be动词 + 形容词/名词 + to do sth.

例：It's important to protect the environment.

（保护环境很重要）

特殊结构：

- It takes sb. some time to do sth.

例：It takes me an hour to finish my homework.

- It's one of the best ways to...

例：It's one of the best ways to learn a language.

- The first thing to do is...

例：The first thing to do is to check the weather.

二、作宾语

直接宾语：

例：She wants to travel around the world.

（她想环游世界）

间接宾语：

例：He asked me to call you last night.

（他昨晚让我给你打电话）

三、作定语

用于修饰名词，表示“做某事的”：

例：

The problem to solve is...

The task for you is...

The purpose of the meeting is...

四、作状语

目的状语：

例：He came to give us a presentation.

（他来给我们做报告）

原因状语：

例：She started to study late because she was late.

（她开始晚睡因为迟到了）

条件状语：

例：If you call me, we'll meet tomorrow.

（如果你给我打电话，我们明天见）

五、作宾语补足语

与动词连用，补充说明宾语的动作：

例：

The teacher asked the students to write an essay.

The manager ordered the meeting to start immediately.

The parents want their children to be responsible.

六、作表语

说明主语的身份、性质或特征：

例：

The best way to learn is through practice.

The real problem is not the task but the attitude.

The goal of the project is to improve communication.

七、特殊结构

疑问词+不定式短语作主语：

例：

- What to do next？

- How to solve this problem？

- Who to invite？

复合不定式作主语：

例：

- The first thing to do is to organize the materials.

- The best way to join the club is to attend the orientation.

注意事项

动词不定式作主语时，谓语用第三人称单数（如"takes"而非"takes"）。

使役动词（如let、make）和感官动词（如see、hear）后接不带"to"的不定式。

形容词作后置定语时，需用"of"搭配（如"a difficult task"）。

通过以上用法，学生可灵活运用动词不定式提升句子表达能力。