Answer:
D.It is not a function because there are two different y-values for a single x-value.
Explanation:
A function is a relation where each input(x) has a single output(y).
From the given graph we can see that there are 2 different values of y i.e. y=-2 and y=4 for single x=4.
Therefore, D is the right answer. The graph is not a function because it is not a function because there are two different y-values for a single x-value.