單項選擇題

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

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單項選擇題

Which of the following statements describes the relationship between flash point and ignition temperature?（）

A.Both are higher than normal burning temperatures
B.The flash point is always higher
C.The ignition temperature is always higher
D.They are not necessarily related

單項選擇題

Flexible hose under pressure in a hydraulic system will （）.

A.tend to twist about its long axis
B.expand in length and in diameter
C.contract in length and expand in diameter
D.flex at right angles to the applied pressure