单项选择题
If a refrigeration compressor will not start, the reason may be （）.
A.the pressure regulating valve is not closing B.an excessive lack of refrigerant in the system C.badly leaking discharge valves D.worn piston rings
单项选择题 Which of the following statements describes the relationship between flash point and ignition temperature?（）
单项选择题 Flexible hose under pressure in a hydraulic system will （）.
单项选择题 An air compressor can be unloaded at start-up by （）.
