Cars buses and bikes stop when the traffic lights turn red.A. canB. mayC. mustD. need

问题补充：

Cars, buses and bikes stop when the traffic lights turn red.

A. can

B. may

C. must

D. need

答案：

A. can

B. may

(答案→)C. must

D. need

解析：考查情态动词：A. can 能够， B. may可以，C. must必须，D. need需要，句意：当交通灯变红的时候汽车，公共汽车和自行车必须停止。选C。