Which of the sets of ordered pairs represents a function?

Question

A = {(2, −2), (5, −5), (−2, 2), (−5, 5)}

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

Answer 1

A is a function, B is not

(4,2), (4,-2) has 2 y values for just 1 x value, B fails the vertical line test for functions