单项选择题
Heavy wear in a particular area of the inner circumference of a packing ring may be caused by （）.
A.a high suction head B.rotating rings C.badly worn bearings D.a loose stuffing box gland
单项选择题 A pressure drop through the refrigerant liquid line may cause （）.
单项选择题 Low compressor head pressure in a refrigeration system can be caused by（）.
单项选择题 Which of the problems listed would came the discharge temperature of an R-12 refrigeration compressor to increase?（）
