语法总结
must 表示必须
must + 动词原形表示必须做某事。
例：People must be careful.
mustn't 表示禁止
mustn't + 动词原形表示不许或禁止做某事。
例：We mustn't play with matches.
must / mustn't 表示规则
must 表示必须，mustn't 表示禁止；后面都接动词原形。
例：We must be careful. We mustn't play with matches.
祈使句安全提示
安全标语常用动词原形开头，否定祈使句用 Don't + 动词原形。
例：Don't smoke! Don't play near fires!
一般现在时讲述故事
故事复述和科普说明常用一般现在时，使情节像画面一样连续呈现。
例：The tiger eats sweets every day. He has a toothache.