90字Students should keep their school clean and tidy. Therefore, they must not spit in public even if no one is around. They also must not throw litter onto the ground because their inconsiderate behavior will dirty the school. When there is no one in the classroom, lights should always be turned off. This will help to save electricity. Moreover, students should always recycle their used papers to save the trees. In conclusion, reduce, reuse and recycle are the ways that students should do to keep the school environment clean.希望能帮助你
