You stop when the traffic light turns red.A. canB. had betterC. needD. must

问题补充：

You stop when the traffic light turns red.

A. can

B. had better

C. need

D. must

答案：

A. can

B. had better

C. need

(答案→)D. must

解析：must是“必须，不得不”，根据下文出现的when the traffic light turns red.可知是“你必须……”。