When the traffic lights are red we stop.A. should B. might C. must D. may

问题补充：

When the traffic lights are red, we stop.

A. should

B. might

C. must

D. may

答案：

A. should

B. might

(答案→)C. must

D. may

解析：交通灯是我们必须要遵守的要求和命令，表示此概念的是must，故选C。