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
网友回答
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。