单项选择题
After putting on a self-contained breathing apparatus，you open the air supply and hear a continuous ringing of a bell. What does this mean?（）.
A.The unit is working properly
B.The face mask is not sealed properly
C.The air bottle needs to be refilled
D.The air supply hose has a leak
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相关考题
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单项选择题
After launching，an inflatable raft should be kept dry inside by（）.
A.opening the automatic drain plugs
B.draining the water pockets
C.using the electric bilge pump
D.using the bailers and cellulose sponge -
单项选择题
A vessel in distress should send by radio telephone the two tone alarm signal followed immediately by the（）.
A.distress position
B.spoken words Mayday，Mayday，Mayday
C.ship's name
D.ship's call letters -
单项选择题
A distress signal（）.
A.consists of 5 or more short blasts of the fog signal apparatus
B.may be used separately or with other distress signals
C.consists of the raising and lowering of a large white flag
D.is used to indicate doubt about another vessel's intentions
