In which set of ordered pairs, (x, y), is y NOT a function of x?
A.
{(7, 10), (10, 7)}
B.
{(7, 10), (5, 10)}
C.
{ (5, 7), (7, 5), (7, 10)}
D.
{(5, 5), (7, 7), (10, 10)}