单项选择题
In a refrigeration system, foaming of the crankcase oil may cause the （）.
A.expansion valve to overfeed B.compressor to knock C.water regulating valve to fail D.crankcase drains to plug
单项选择题 Excessive scale formation in a distilling plant may result from （）.
单项选择题 Foaming of the oil in a refrigeration compressor crankcase is caused by （）.
单项选择题 Which of the listed characteristics can be applied to R- 12 vapor?（）
