單項選擇題Which of the valves listed should be used either in the fully opened or the fully closed position?（）
A.A gate valve
B.A globe valve
C.Any check valve
D.Any needle valve
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1.單項選擇題If a refrigeration compressor is running continuously without lowering the temperature in the refrigerated space, the trouble may be （）.
A.a shortage of compressor oil
B.warm food in the refrigerator
C.excessive condenser cooling water
D.a shortage of refrigerant
2.單項選擇題In the design of hydraulic piping and equipment consideration is given to minimize turbulence in the hydraulic fluid, as this will cause （）.
A.molecular fluid vibration
B.energy losses
C.wide pressure variations
D.mechanical damage to control valves
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