Which of the following graphs is not a function?
a.
On a coordinate plane, a parabola opens up and goes through (negative 2, 1), has a vertex at (0, 0), and goes through (2, 1).
c.
On a coordinate, a cubic root function approaches y = negative 3 and y = 3.
b.
On a coordinate, plane a cubic root function approaches x = negative 3 and x = 3.
d.
On a coordinate plane, a parabola opens to the right and goes through (1, 1), (0, 0) and (1, negative 1).