情态动词 must — 英语填空题
题目
在横线上填入 must 或 mustn't，使句子符合道路安全规则。 1. To cross the road safely, we ___ look at the traffic lights first. 2. You ___ run on the road, because it's very dangerous. 3. We ___ wait on the pavement and look for a zebra crossing.