Remember when you got that question in math about an input-output table, saying that this couldn't happen?
x y
1+1 =1
2+1=2
3+1=4
3+1=5
4+1=5
5+1=6
That's because two y values cannot be obtained by the same x-value. On the graph, graphically it shows this when there are two points (4,4) and (4,-2). This cannot happen.
The answer that you're looking for is the last answer choice. Great question!