试一试: Woman: Can we go to the movies tonight? Man: Sorry, I can't. I ___ work late tonight. 选出那个男人会说的话。 (have to / don't have to / can) 答案: have to — 他因为工作去不了，所以他说 I have to work。
must：严格的规定
must + 动词，是很严格的规定。你会在标志和表格上看到它。
Drivers must stop here.
You must be 18 or older.
试一试: Woman: Can I pay for the class later? Man: No, sorry. It says here that you ___ pay before the first class. 选出那个男人会说的话。 (must / can't / don't have to) 答案: must — 纸上写着不能以后再付，所以第一节课前必须付：must。
can't、not allowed to：不可以
不能做某件事的时候，美国人常说 can't 或 not allowed to + 动词。
You can't go in there.
We're not allowed to wear jeans at work.
试一试: Woman: Why is the manager talking to that man? Man: He has his dog with him. Dogs ___ be in the store. 选出那个男人会说的话。 (can't / have to / must) 答案: can't — 经理拦住了带狗的男人，所以狗不能进店：can't。
书面规定：must not
书面规定里常写 must not + 动词。
You must not be late.
Visitors must not feed the animals.
试一试: Woman: Read rule number 3. Man: 'Students ___ eat or drink in the computer room.' 把规则补充完整。 (must not / must / don't have to) 答案: must not — 食物和饮料对电脑不好，所以规定写着学生在那里不许吃喝：must not。
mustn't：缩写形式
mustn't 是 must not 的缩写，在英式英语里听得更多。美国人通常说 can't。
You mustn't open this door.
试一试: Woman: It's seven, so we ___ swim here. Look at the sign: 'You must not swim after six.' Man: Oh. Then let's come back tomorrow. 选出那位女士会说的话。 (can't / should / don't have to) 答案: can't — 牌子上写的是 must not，美国人会说 can't。不是 don't have to。
是不允许，还是没有规定？
不能做，用 can't 或 not allowed to；可以自己选，用 don't have to。
You can't take these books home.
You don't have to answer every question.
试一试: Man: Do I have to come to class on Thursday? Woman: No, you ___ come. It's an extra class. Come if you want. 选出那位女士会说的话。 (don't have to / aren't allowed to / must) 答案: don't have to — 这是一节额外的课，来不来他自己选，所以他不必来：doesn't have to。