单项选择题
A C02 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 contra-guide is a type of（）.
单项选择题 A dead reckoning (DR) plot（）.
单项选择题 A deck fitting, used to secure line or wire rope, consisting of a single body with two protruding horns is called a（）.
