Correct option is C
In the milling method, the mechanical force applied to two material particles to create a rubbing action that turns them into powder is attrition. Attrition involves frictional or rubbing forces between particles or between a particle and a surface, gradually reducing particle size into fine powder.
Impact involves striking, shear involves sliding layers, and compression involves pressing, but the rubbing action specific to milling is attributed to attrition.
