Consider the following statements with reference to grinding wheel characteristics:
(i) Aluminum oxide and silicon carbide are used for making the grinding wheels.
(ii) Rubber bonds are used for making flexible wheels.
(iii) The grade of a wheel is determined by the strength of the bonding materials.
(iv) Negative rake angles are used for grinding of high-strength materials.
Which of the above statements are correct?
(a) 1, 2 and 3 (b) 1, 2 and 4
(c) 1, 3 and 4 (d) 2, 3 and 4