单项选择题
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
单项选择题 Class C fires are best extinguished by （）.
单项选择题 Class B fires are best extinguished by smothering, i-e（）.
单项选择题 Class A fires are best extinguished by quenching or cooling with （）.
