Iwill mark brainliest who ever hepls!

which set of ordered pairs represents a function?

a) {(0, 1), (1, 3), (1, 5), (2, 8)}

b) {(0, 0), (1, 2), (2, 6), (2, 8)}

c) {(0, 0), (0, 2), (2, 0), (2, 4)}

d) {(0, 2), (1, 4), (2, 6), (3, 6)}