Which of the following case hardening processes, result in a change in the composition in a steel component?
(1) Carburizing (2) Cyaniding
(3) Nitriding (4) Flame hardening
(a) 2, 3 and 4 only (b) 1, 3 and 4 only
(c) 1, 2 and 3 only (d) 1, 2, 3 and 4