读一读，选择适当的词填空。

are    three    rules    left    right    green    red    yellow

    You must know the traffic if you walk in a city. The traffic lights are the same in every city. There always lights. You can cross the street at the light and you must stop and wait at the light. The light means "Slow down and stop". If you drive a car, you must drive on the side of the road in China. But in England, people drive on the side of the road.