We mustn't write on the walls.

我们绝不能往墙上写。

同一单元的其他句子

• Don't eat in the classroom, please.请不要在教室里吃东西。
• We must not run in the hallways.我们不允许在走廊里奔跑。
• Can I listen to music in class?我可以在课堂上听音乐吗？
• You have to wear the school uniform.你必须穿校服。
• Don't be late for school.上学不要迟到。