1.Which of the following sets of ordered pairs defines a function?
a. {(3, 2), (-3, 6), (3, -2), (-3, -6)}
b. {(1, 2), (2, 6), (3, -2), (4, -6)}
c. {(2, 2), (2, 3), (2, 4), (2, -9)}
d. {(4, 4), (-3, 4), (4, -4), (-3, -4)}