Which of the relations below is not a function? mark that apply.

a) {(-1, -1), (7, 7), (3, 3), (4, 4)}
b) {(6, 3), (6, 4), (6, 9), (6, 12)}
c) {(3, 6), (4, 6), (9, 6), (12, 6)}
d) {(2, -2), (-2, 2) (3, 1), (1, -3)}
e) {(0, 5), (0, 2), (4, 2)}