Which of the following relations is a function?

O {(9,0), (10,3), (11, 6), (11, 9)}
O {(1, 1), (1, 2), (1, 3), (1,4)}
O {(1, 3), (2, 10), (6, 24), (24, 6)}
O {(0,6), (-1, 10), (-1, 14), (-3, 18)}