Which of the following relations is in Third normal form (3NF)? Give sufficient reasoning if not in 3NF. (a) R(ABCD) F = {ACD → B; AC → D; D → C; AC → B} (b) R(ABCD) F = {AB → C; BCD → A; D → A; B → C} (c) R(ABCD) F = {AB → C; ABD → C; ABC → D; AC → D} (d) R(ABCD) F = {C → B; A → B; CD → A; BCD → A}