单项选择题Which is the proper method of determining whether a portable CO2 fire extinguisher needs recharging?()
A.Check the tag to see when the extinguisher was last charged
B.Release a small amount of CO2; if the CO2 discharges,the extinguisher is acceptable
C.Weigh the extinguisher and compare the weight against that stamped on the valve
D.Recharge the extinguisher at least once each year