單項選擇題The percentage of impurities in a specific fuel oil sample is determined by ().

A.settling in a fuel tank
B.testing in a laboratory centrifuge
C.burning in a calorimeter
D.testing in a closed cup


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2.單項選擇題Which of the following statements is correct concerning the “flash point ” of a liquid?()

A.It is lower than the ignition temperature
B.It is the temperature at which a substance will spontaneously ignite
C.It is the temperature at which a substance, when ignited, will continue to bum
D.It is the temperature at which the released vapors will fall within the explosive range

3.單項選擇題Sludge may form in the crankcase of an air conditioning compressor as a result of ().

A.bubbling refrigerant
B.overheating and oxidation
C.lowered operating temperatures
D.reducing the cloud or flash point

5.單項選擇題Excessive circulation of the lubricating oil with the refrigerant in a refrigeration system will cause ().

A.carbon deposits on the compressor suction valves
B.the evaporator temperature to increase
C.rapid corrosion of the thermal expansion valve
D.no operating problems