Which represents a function?

A {(-2, 1). (0, 2), (1,3), (1.4)}

B {(-1,5),(-1,6). (1,5), (1.6)}

C
{(3, 1). (3. 4). (3.5), (3,9)}

D{(4.8). (5. 1). (7.3).(8.6)}

Need Help ASAP