traffic light和 traffic lights 区别

把“红绿灯”看成一个整体时，用traffic light，单数。表达它有三盏灯时，用three lights，复数。

The traffic light has three lights， red， yellow and green.

红绿灯有三盏灯，红灯、黄灯，和绿灯。

Red is on top， yellow is in the middle， and green is on the bottom.

红灯在上面，黄灯在中间，绿灯在下面。

注：on top和on the top都可以，但是on bottom不行。