Which of the sets of ordered pairs represents a function?

Question

A = {(1, −2), (3, −5), (5, 2), (7, 5)}

B = {(4, 2), (4, −2), (9, 3), (9, −3)}

Only A
Only B
Both A and B
Neither A nor B

Answer 1

if two pairs have the same first value, the relation is not a function.
so, what do you think?