Which set of ordered pairs is NOT a function ?
{(3, 2) (4, 1) (5, 2) (8,8) }
{(3, 6) (2, 1) (6, 2) (5,9)}
{(7,3) (8, 2) (3,6) 7,4)}
(4.4) (5, 4) (1,4) (7,4)}