He knows it is high time that he at once.A. quits smokingB. quitted smokingC. should quit

问题补充：

He knows it is high time that he at once.

A. quits smoking

B. quitted smoking

C. should quit to smoke

D. quitted to smoke

答案：

A. quits smoking

(答案→)B. quitted smoking

C. should quit to smoke

D. quitted to smoke

解析：本题考查虚拟语气及动词用法。it is high time that + 主语 + 过去时态/should + v原形；quit doing 放弃做。故选B。