用所给词的适当形式填空，使短文内容完整通顺。方框中有两个词是多余的。

if, until, but, make, at, accident, be, green, left, right, red, go

This is a street crossing. There are red and green traffic lights  each crossing. Drivers must     careful to watch them.
When the traffic light is   , the cars may go. When the light turns   , the cars must stop. They must wait（等待）  the red light turns green. Then they can go on. Sometimes the drivers want     a right turn or a left turn. They can make a   turn when the light is green or red.    they shouldn’t drive too fast.  they want to make a left turn, they must wait until the traffic light is green. There may be    if drivers don’t obey the traffic rules. All of the drivers should be very careful when they are driving on the road.