单项选择题
Which of the problems listed could be indicated if a sight glass in the refrigerant liquid line is full of bubbles?（）
A.Proper refrigerant charge B.Faulty expansion valve C.Insufficient refrigerant D.Solenoid valve stuck open
单项选择题 Moisture in a refrigeration system can cause （）.
单项选择题 When the propeller blades are integral with the hub, the propeller is called a （）.
单项选择题 The tendency of a flammable liquid to vaporize is indicated by its （）.
