Which of the following represents a relation that is not a function?
A.
x -7 -5 -7 1
y 33 31 39 33


B.
x 8 -5 13 -7
y 33 31 39 33


C.
x -7 -5 -1 1
y 33 31 39 33


D.
x -7 -5 8 13
y 33 31 39 33