Which of the following chocies is not a function?

A {(0, 0), (1, 4), (2,8)}
B {(0, 0), (3, 16), (16, 49)}
C {(1, 1), (2, 2), (3, 3), (4,4)}
D {(7, 1), (6, 2), (5, 3), (5,4)}
E All of these choices are functions.