單項(xiàng)選擇題

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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單項(xiàng)選擇題

Class C fires are best extinguished by （）.

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

單項(xiàng)選擇題

Class B fires are best extinguished by smothering, i-e（）.

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