1. There Be 句型（表示“存在”）
There be 用于表达“某处有某物/某人”，强调存在而非拥有。
- There is + 单数名词 / 不可数名词
- There are + 复数名词
There is a book on the table.
There are many students in the classroom.
注意：be 动词的形式由其后的名词决定（就近原则）。
There is a pen and two books. ✅
There are two books and a pen. ✅
2. To Do（不定式）
不定式（to + 动词原形）常表示目的、将来动作或抽象概念。
常见用法：
- 作主语：To learn English is important.
- 作宾语：I want to go.
- 作目的状语：She studies hard to pass the exam.
- 形容词后**：It’s easy to understand.
My dream is to become a teacher.
3. Doing（动名词）
动名词（动词 + ing）具有名词性质，常表示习惯性、正在进行或泛指活动。
常见用法：
- 作主语：Swimming is good exercise.
- 作宾语：I enjoy reading.
- 介词后**：She is good at drawing.
- 固定搭配**：finish, avoid, consider, suggest 等后接动名词
He avoids eating junk food.
4. To Do vs. Doing — 关键区别
某些动词后接 to do 或 doing 意义不同：
- remember to do：记得要去做（未做）
Remember to lock the door.（记得去锁门） - remember doing：记得做过某事（已做）
I remember locking the door.（我记得锁过门了） - stop to do：停下当前事去做另一件事
He stopped to talk to me.（他停下工作来和我说话） - stop doing：停止正在做的事
He stopped talking.（他停止说话）