（） are formed by abrasive particles entering the bearing and scoring the shaft.
A . Grooves B . Recesses C . Ridges D . Ni
磨蚀作用（abrasion）
To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.
A . lantern rings B . bearings C . easing volutes D . wearing ring
Which of the following processes is NOT an abrasive machining process?
