单项选择题
A.面心立方B.金刚石立方C.体心立方
A.WP≤0.045%,WS≤0.055%B.WP≤0.040%,WS≤0.040%C.WP≤0.035%,WS≤0.030%
A.电极轮必须成对更换B.电极轮上下轮必须大小相似C.电极轮有圆面朝内