This problem may lead to more serious ones if unsolved.A. makingB. leftC. remainedD. keepi

问题补充：

This problem may lead to more serious ones if unsolved.

A. making

B. left

C. remained

D. keeping

答案：

A. making

(答案→)B. left

C. remained

D. keeping

解析：考查状语从句的省略句：句意：这个问题可能或导致更严重的病如果被任由不治疗的话。If left unsolved=if the problem is left unsolved，如果主从句主语一致的时候，可以省略从句的主语和be动词，选B。