交通信号灯

摘要

＜正＞不闯红灯是我们每个人都应该遵守的交通规则。关于交通信号灯,你知道多少呢?The green light allows cars to go.The yellow light tells the drivers that the signal willchange to red soon.The red light stops any traffic.You must know these rules.But do you know thatthere was no yellow light until the 1920s?With only red and green lights,drivers didn’t have