Select the sets that are not functions.

B = {(1, 2), (2, 1), (3, 0), (4, -1)}
D = {(1, 1), (1, 2), (1, 3), (1, 4)}
A = {(1, 2), (2, 3), (3, 4), (4, 5)}
C = {(-1, 3), (0, 3), (1, 3), (2, 3)}
E = {(6, 2), (7, 3), (6, -1), (5, 4)}