单项选择题
A.drain water from the air receiver
B.drain water from the cylinders
C.delay the compression process until the motor is up to speed
D.check pump alignment
单项选择题 Personnel working with refrigeration systems, and subject to the exposure of refrigerants should wear （）.
单项选择题 To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.
单项选择题 If the capacity of a centrifugal pump decreases gradually over a long period of time, you should replace the （）.