选择合适的单词将短文补充完整，每词只用一次。

a   in   are   three   rules   left   night   green   red   yellow

    You must know the traffic if you walk 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 car, you must drive on the side of the road in China. But in England, people drive on the side of the road.