关于“保持教室干净，我们不能乱扔垃圾”的英语翻译，综合权威信息整理如下：

一、基础翻译

1. 直接翻译

We must not litter anywhere.

Please do not litter.

2. 完整句子

We must keep the classroom clean and tidy.

Let's maintain a clean classroom environment.

二、扩展表达

1. 行为规范类

Keep the classroom clean, we must not litter, and do垃圾分类.

No spitting, no littering, no disorder.

2. 奖惩机制类

Reward those who keep the classroom clean, punish those who litter.

Good behavior in class is rewarded, littering results in a penalty.

三、标语参考

"Keeptheclassroomclean. Be quiet on class. Don't throw rubbish casually."

"除了文明，什么也别留下!"

建议优先采用简洁明了的表达，如"Keep the classroom clean, we must not litter"，既符合英语表达习惯，又能有效传达核心信息。同时，可结合班级特色设计标语，增强教育意义。