單項選擇題The sealing function of the piston ring is brought about by the gas pressure above and behind the piston ring, which forces it （） against the bottom of the ring groove, and （） against the cylinder wall.

A.upwards；inwards
B.upwards；outwards
C.downwards；inwards
D.downwards；outwards


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1.單項選擇題The scavenge port inspection should be carried out（）, to obtain the most reliable result with regard to the effectiveness and sufficiency of the cylinder lubrication and the combustion cycle (complete or incomplete).

A.at the first stop after a long voyage egby anchoring if possible
B.at the first stop after arrival at harbor
C.at the first stop after low load running
D.at the first stop after passing river or canal passage

3.單項選擇題In general, the oil mist defectors include a base plate with air blast pumpThe function of air blast pump is to （）crankcase.

A.supply clean air to the measuring compartment of the units for more accuracy
B.generaate the pressure required for the extraction of the oil mist from the
C.generate the pressure required for the extraction of the oil mist from the crankcase
D.supply clean air to the measuring track of the units for more accuracy

4.單項選擇題In general, the oil mist detectors include a built-in heating unit and a compact plug for electrical connectionThe function of heating unit is to （）

A.avoid false alarms as a result of condensing water vapor
B.avoid danger of frost under very cold weather
C.reduce the viscosity of the crankcase atmosphere in order to improve the fluidity
D.keep the temperature of the oil mist detectors in an appropriate range

5.單項選擇題（）continuously extract the crankcase atmosphere, via a pipe system, and move it past a sensitive and accurate opacity measuring track.

A.The oil mist detectors
B.The smoke detectors
C.An oily water monitor
D.Oil discharge monitoring and controlling system