氟气通过NaOH溶液形成氟化钠，同时放出一种无色气体X，X由两种元素组成，其中氯元素的质量分数为70.4%，则下列有关说法正确的是(    )

A．X气体是HF

B．X气体是OF₂

C．氟气既是氧化剂又是还原剂

D．NaOH既不是氧化剂又不是还原剂

Carbon dioxide as a fire fighting agent has which advantage over other agents?（）.

A.It causes minimal damage

B.It is safe for personnel

C.It is cheaper

D.It is most effective on a per unit basis