单项选择题
A.Hydraulic B.Mechanical C.Pneumatic D.Electrical
Which of the following statements concerning energy is ...
单项选择题Which of the following statements concerning energy is correct?（）
A.Energy can be created or destroyed B.Energy may not be transformed C.The total quantity of energy in the universe is always the same D.None of the above
In a compression refrigeration cycle, the temperature o...
单项选择题In a compression refrigeration cycle, the temperature of the liquid refrigerant experiences its greatest decrease in the（）.
A.evaporator B.compressor C.expansion valve D.condenser
Excessive oil foaming in the crankcase of a refrigerati...
单项选择题Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur（） when the compressor.
A.has continuously for a long period B.suction pressure is below normal C.oil level is below normal D.starts after a long idle period
