单项选择题
A CO2 portable extinguisher is annually checked by（）.
A.reading the gage pressure B.weighing the extinguisher C.discharging a small amount of CO2 D.seeing if the seal has been broken
单项选择题 A CO2 extinguisher on a ship which has lost 10% of its charge must be（）.
单项选择题 A branch line valve of a fire extinguishing system on a ship must be marked with the（）.
单项选择题 （），as the chemical extinguisher agent，should be used for an electric fire.
