Assertion (A): The grade of grinding wheel is a measure of hardness of the abrasive used for the wheel
Reason (R): Grading is necessary for making right selection of the wheel for a particular work
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false but R is true