单项选择题
A.1~1/2 B.1/2~1/3 C.1/3~1/4 D.1/4~1/5
A.15° B.20° C.30° D.45°
A.工件生锈 B.锉刀打滑 C.锉刀生锈 D.破坏加工表面的粗糙度