must/mustn't表达行为规范 — 英语填空题
题目
根据提示，用 must 或 mustn't 完成句子：上学路上过马路前必须先看红绿灯；在马路上不能追逐打闹；乘坐公交车时必须排队上车。Tom 想做一名 good student，请补全句子：Before crossing the road, you ___ look at the traffic lights. You ___ run and play on the road. You ___ wait in line when you get on the bus.