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

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单项选择题

A.foam extinguishers
B.water spray equipment
C.dry powder extinguishers
D.soda-acid extinguishers

单项选择题

A.deprival of oxygen
B.removal of heat
C.spraying of water
D.injecting of soda-acid

单项选择题

A.deprival of oxygen
B.a water spray
C.soda-acid
D.foam