When air is at its dew point it is at ...

单项选择题When air is at its dew point it is at its（）

A.lowest absolute humidity
B.lowest relative humidity
C.highest absolute humidity
D.highest relative humidity

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1.单项选择题If you find an extremely large refrigerant leak while using a halide torch, your flame will（）

A.change from blue to orange
B.‘flare up’ and remain lighted
C.probably go out
D.stay blue

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2.单项选择题Before charging a refrigeration unit, the refrigerant charging lines should be（）

A.flushed with clean refrigerant oil
B.purged with the refrigerant
C.washed with an ammonia and alcohol solution
D.grounded to compressor

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3.单项选择题In the presence of an open flame or hot surfaces, chlorinated fluorocarbon refrigerants decomposes and from （）

A.petroleum crystals
B.phosgene gas
C.water vapor
D.carbon monoxide

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4.单项选择题In an operating refrigeration system low on refrigerant, a liquid line sight glass will（）

A.be clear
B.be blue
C.be light green
D.show bubbles

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5.单项选择题The thermal expansion valve reacts directly to the （）

A.temperature in the space being cooled
B.liquid refrigerant pressure at the solenoid valve
C.pressure drop across the evaporator coils
D.refrigerant gas superheat at the coil outlet

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6.单项选择题When transmitted by a reduction gear, diesel engine speed is reduced and the torque available for work （）

A.remains the same
B.is reduced
C.is increased
D.is eliminated

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7.单项选择题Pitting in the area close to the pitch line and on the same end of each gear tooth of a reduction gear unit would be caused by （）

A.corrosion on the gears
B.excessive gear speed
C.dirt in the oil
D.misalignment of the gears

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8.单项选择题When used with reversing reduction gears, medium-speed diesel engines should be bolted to their foundations with fitted bolts at the drive end and clearance(loosely fitted) bolts in other locations √This is done to （）

A.maintain alignment when the ship’s hull is working in heavy seas
B.ensure engine vibrations correspond to the natural frequency of the hull
C.permit the engine to expand away from the driven equipment as the engine heats up and expands
D.maintain engine thrust bearing clearances

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9.单项选择题Some medium and high-speed diesel engines require reduction gear units to provide a useful propeller speedIn most reduction gears, the bull gear（）

A.must churn the oil in the sump
B.is connected to the propeller shaft
C.is driven at the highest RPM
D.compensates for alignment variations between the engine and pinion gear

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10.单项选择题A four-stroke cycle, turbocharged, 1000 horsepower diesel engine has been operating under loadThe load suddenly increases, causing excessive black exhaust smoke, and a rapid rise in the lube oil temperatureIn response to this condition, you should:（）

A.reduce load
B.check your exhaust
C.adjust cooling water temperature
D.increase lube oil flow

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