to 后面加 do 还是 doing？to 的两重身份 + 判断口诀（to 后能加 it → doing）
引言
很多同学一看到 to 就填动词原形，一考试就踩坑。抖音老师用一句话点破：to 有两重身份，一个是不定式符号，一个是介词。
to 的两重身份
```text
身份一：不定式符号 → to do
want to do / decide to do / hope to do
身份二：介词 → to doing
pay attention to doing / look forward to doing
```
介词后面要接宾语，动词不能直接做宾语，所以要变成动名词 doing。
判断技巧：to 后面能不能加 it？
```text
能加 it（代词可作介词宾语）→ to 是介词 → 加 doing
不能加 it → to 是不定式符号 → 加 to do
```
```text
pay attention to it ✔ 注意它
→ pay attention to doing
look forward to it ✔ 盼望它
→ look forward to doing
want to it ✘ 想要它（说不通）
→ want to do
```
常考短语：介词 to + doing
```text
pay attention to doing 注意做某事
look forward to doing 盼望做某事
stick to doing 坚持做某事
devote to doing 致力于做某事
be used to doing 习惯做某事
object to doing 反对做某事
the key to doing 做某事的关键
thanks to doing 多亏做了某事
```
常考搭配：不定式 to do
```text
want to do 想要做
hope to do 希望做
decide to do 决定做
try to do 尽力做
promise to do 承诺做
forget to do 忘记去做
```
一张表总结
```text
to 的身份 后面接 例子
不定式符号 to do want to do
介词 to doing pay attention to doing
```
```text
判断口诀：
to 后能加 it → doing
to 后加不了 it → to do
```
实战练习
```text
- We should pay attention to ______ (protect) the environment.
→ protecting（介词 to，缺宾语）
- I'm looking forward to ______ (see) my old friend.
→ seeing（介词 to）
- She wants ______ (buy) a new bike.
→ to buy（不定式）
```
总结
```text
to 有两重身份：
不定式符号 → to do
介词 → to doing
判断方法：to 后面能不能加 it？
能加 it → doing；不能 → to do
```
```text
今日小抄：
pay attention to doing 注意做某事
look forward to doing 盼望做某事
want to do 想要做某事
```