题目

Every year many people lose their lives on the roads. And about one or two hundred thousand people get hurt in road accidents.There are rules to make road safe, but people do not obey the rules. If everybody obeys the rules, the roads will be safer. How can we make the road safe?Remember the rules. In England, traffic is on the left of the road. Cars, buses and bikes must keep on the left side of the road. But in most countries traffic keeps on the right.Before crossing the road, stop and look both ways. Look right and left. Then, if you are sure that the road is clear, you can cross the road; 如图所示，螺线管B置于闭合金属环A的轴线上，当B中通过的电流减小时，则 A．环A有缩小的趋势 B．环A有扩张的趋势 C．螺线管B有缩短的趋势 D．螺线管B有伸长的趋势