Which of the following is not a function?
(A) {(1, 2), (-2, 2), (3, 3)
(B) {(1, 2), (-2, 6), (3, 3)
(C) {(2, 2), (2, 3), (4,3)}
(D) {(1, 3), (2, 3), (4,3)}
(E) None of the above