168. Whenever I met him, _____ was fairly frequent, _____ I liked his sweet and hopeful smile.

A．that; that

B．which; /

C．it; that

D．it; so

不安全环境是事故发生的原因之一，环境可分为（）。

A、社会环境

B、自然环境

C、生产环境

D、气候环境