Which set is a function?
a) {(0,3), (3,0), (0,4), (4,0)}
b) {(0,2), (2,0), (4,6), (6,4)}
c) {(2,6), (3,6), (4,6), (2,0)}
d) {(6,2), (2,0), (4,6), (6,4)}