Tom does speak Chinese well, but his reading and writing skills leave much .
A. to improve
B. to be improved
C. improving
D. improved
网友回答
A. to improve
(答案→)B. to be improved
C. improving
D. improved
解析：improve与much之间存在被动关系，且还未发生；若用improved，则表示已完成。故选B。