单项选择题
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
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A.molecular fluid vibration
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Which of the conditions listed represents the greatest effect of excess frost accumulation on the evaporator coils?（）
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B.Reduces the efficiency of the plant
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