单项选择题
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
单项选择题 In a compression refrigeration cycle, the temperature of the liquid refrigerant experiences its greatest decrease in the（）.
单项选择题 Excessive oil foaming in the crankcase of a refrigeration compressor is most likely to occur（） when the compressor.
单项选择题 Strainers are commonly used in hydraulic systems to （）.