Ifunsolved the problem of food safety may lead to more serious results.A. having leftB.

问题补充：

Ifunsolved, the problem of food safety may lead to more serious results.

A. having left

B. to leave

C. left

D. leaving

答案：

A. having left

B. to leave

(答案→)C. left

D. leaving

解析：句意：如果食品安全问题被任由不解决，就会导致更严重的后果。这是一个状语从句的省略句，完整的句子是：If the problem of food safety is left unsolved，当主从句的主语一致的时候，可以省略从句的主语和be动词，选C。