Trafficlightsarered,yellowandgreen.Theyareveryimportant...
問題詳情：Trafficlightsarered,yellowandgreen.Theyareveryimportantsignals(信號).TrafficlightsareusuallyplacedatbusystreetcornerstohelpcontroltrafficSometimes,theyareonstreetsnearschoolsandshops,too.Mosty...