Question

Many provinces have been hit with smog. If _______ unsolved, the problem may lead to more serious results.

A．having left

B．to leave

C．left

D．leaving

Answer 1

C

试题分析：句意：很多省份都遭遇了雾霾，如果任由问题不解决，它会导致更严重的后果。这里if条件句是省略式，完整的是If the problem is left unsolved，…，如果主从句的主语一致的话，可以省略从句的主语和be动词，所以选C。