— _________, this math problem seemed quite simple to me, but when I tried to work it out, I just couldn’t.

— There are always things like this, I think.

A．On one hand

B．In my opinion

C．At first sight

D．On its own

根据《危险化学品安全管理条例》______必须为危险化学品事故应急救援提供技术指导和必要的协助。

A．危险化学品审查单位

B．危险化学品研制单位

C．危险化学品生产企业

D．危险化学品储存单位