单项选择题
A.excessive pump speed
B.excessive suction head
C.worn wearing rings
D.gross pump misalignment
单项选择题 Which of the following statements is correct relative to distillation plant operation?（）
单项选择题 The amount of moisture in a given sample of air, when compared with the amount of moisture the air could hold if totally saturated at the existing temperature of the sample, is called （）.
单项选择题 The purpose of an air compressor unloading device is to （）