Which of the following relations ia a function?
A
{(0,1), (0,2), (0,3), (0,4)}
B
{(1,6), (1,7), (7,8), (8,9)}
С
{(2,3), (3,2), (2,4), (4,2)}
D
{(1,1), (3,2), (6,3), (8,4)}