A = {a, b, c, d] X = {1, 2, 3, 4) The function f:A?X is defined by the arrow diagram below. Select the set of pairs that defines a function that is equal to f. a 2 3 4 f f = {(a, 2), (b, 3), (c, 4), (d, 4)) f = {(a, 2), (b, 3), (d, 2)} f = {(a, 1), (b, 3), (c, 4), (d, 4)) f = {(a, 2), (b, 3), (c, 4), (d, 2)} d