must have done 还是 can't have done？情态动词对过去推测的中考真题
引言
情态动词表推测还有更难的考法——对过去的事情做推测，结构是"情态动词 + have done"。
中考真题里经常考：到底选 must have done 还是 can't have done？方向判断错了，整题就丢了。抖音上一条「选 must 还是 can't？」视频把这个考点讲透了。
中考真题
```text
George ______ too far. His coffee is still warm.
A. must have gone
B. might have gone
C. needn't have gone
D. can't have gone
```
答案：D. can't have gone
怎么判断方向
后半句是证据：
```text
His coffee is still warm.（他的咖啡还热着。）
```
咖啡还热 → 他刚走不久 → 根本走不远 → "不可能走很远"
所以用 can't have done（不可能做过）。
两个核心结构
```text
过去一定做过 → must have done
过去不可能做过 → can't have done
```
```text
He must have finished his homework.
（他一定已经写完作业了。——书桌上没有作业本）
He can't have gone to school. It's Sunday.
（他不可能去上学了，今天是周日。）
```
可能做过：may / might have done
```text
She might have forgotten the meeting.
（她可能忘了这个会。——不确定）
He may have left the key at home.
（他可能把钥匙落在家里了。——不确定）
```
避坑提醒
mustn't have done 不是"不可能"
```text
mustn't = 禁止（不是推测）
```
```text
错：He mustn't have gone there.（想表达"不可能"）
对：He can't have gone there.
```
否定推测只认 can't have done。
needn't have done 是"本不必做"
```text
needn't have done = 本来不必做（但做了）
```
```text
You needn't have bought the ticket.（你本不必买票的。——但买了）
```
这不是推测，别混用。
一张表总结
```text
结构 意思
must have done 过去一定做过
can't have done 过去不可能做过
may/might have done 过去可能做过
mustn't have done 禁止（非推测）
needn't have done 本不必做
```
总结
情态动词 + have done 做题顺序：
```text
- 先看证据是肯定还是否定
- 肯定证据 → must have done
- 否定证据 → can't have done
- 不确定 → may/might have done
```
```text
今日小抄：
must have done 一定做过
can't have done 不可能做过
might have done 可能做过
mustn't ≠ 不可能 （是禁止）
```