Which relation shown as ordered pairs is a function?
O {(1, 4); (2, 4); (1, 16); (4, 25)}
O {(4. 14); (7.25); (3, 32); (4, 23)}
O {(2, 3); (2, 5); (2, 6); (2, 7)}
O {(3, 3); (4,3): (5,3): (6,3)}