祈使句时态用一般现在时，do的一般现在式就是 do ,否定加not ，就是don't .也可以：You mustn't eat in class. 语气缓和一点的是：You shouldn't eat in class.
Don't eat in class.课堂上不要吃东西。祈使句的否定句在句子开头加 Don't
