Which of the following ordered pair could NOT be included in this set if it is a function?
{(-4, 2), (3, 6), (4,3), (x, y) }
A (x, y) = (-3, 6)
B (x, y) = (1, 2)
C (x, y) = (3,6)
D (x, y) = (4, -3)