PLEASE HELP!!! WILL GIVE BRAINLIEST ANSWER

Which relation is a function?

A {(2, 3), (1, 5), (2, 7)}
B {(-1, 5), (-2, 6), (-3, 7)}
C {(11, 9), (11, 5), (9, 3)}
D {(3, 8), (0, 8), (3, -2)}