we mustn't walk on the grass.
we mustn't waste the water.
we must keep the water clean.
we mustn't throw the rabishes.
wu must keep the earth clean.在加几句话，，，，，，教室里的规则也帮忙弄下谢谢We mustn't pollue the earth.we mustn't run in the ciassroom.we must study hard.教室的规则在加4句话