Tom does speak Chinese well but his reading and writing skills leave much .A. to improveB

问题补充：

Tom does speak Chinese well, but his reading and writing skills leave much .

A. to improve

B. to be improved

C. improving

D. improved

答案：

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。