【单选题】
The soda-acid portable extinguishers must be discharged and refilled （）.
A、every six months
B、every year
C、every one and half year
D、every two years
查看正确答案
A、Dry chemical and carbon dioxide B、Foam (stored pressure) and soda-acid C、Carbon dioxide and foam (stored pressure) D、Dry chemical and soda-acid
