Why is the set {(3,6), (4,8), (5 , 10), (3, 1), (6, 12), (7, 10)} NOT a function?
A. The ordered pairs are not in ascending order.
B. The ordered pairs do not all follow the rule y = 2x.
С. 3 is mapped to both 1 and 6.
D. Both 5 and 7 are mapped to 10.