单项选择题
A.face shield
B.a respirator
C.rubber gloves
D.an all purpose gas mask
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 （）.
单项选择题 Distilled water from an evaporator may be discharged into a potable water tank （）.