單項選擇題After each reading of an oxygen indicator, the instrument should be purged with（）.

A.CO2
B.fresh air
C.the tested compartment's air
D.water


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1.單項選擇題After extinguishing a fire with C02,it is availabe to（）.

A.use all CO2 available to cool the surronding area
B.stand by with water or other agents
C.thoroughly ventilate the space of CO2
D.jettison all buring materials

2.單項選擇題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

3.單項選擇題After using a C02 portable extinguisher,it should be（）.

A.put back in service if some CO2 remains
B.hydrostatically tested
C.retagged
D.recharged

4.單項選擇題All dunnage planks and mats must be sent to board（）commencement of loading.

A.prior to
B.during
C.in the period of
D.afterwards

5.單項選擇題All echo-sounders can measure the（）.

A.actual depth of water
B.actual depth of water below keel
C.average depth from waterline to hard bottom
D.average depth of water to soft bottom