单项选择题
A.flooding back
B.superheating
C.overflowing
D.recycling
单项选择题 What is a function of the wearing rings used in most centrifugal pumps?（）
单项选择题 If air at 95℃ dry bulb temperature and 50% relative humidity is conditioned to 75℃ dry bulb temperature and 50% relative humidity, it is an example of （）.
单项选择题 Which of the following descriptions best identifies the operating principal of a flash-type evaporator?（）