The graph of this relation is four points on the coordinate plane (see attached diagram).
A function is a special relation, where each input x has a single output y.
This relation is not a function, because for one x (x=-1), here are two different possible y (y=3 or y=2). If you consider the graph, you can see that there will be vertical line passing through the points (-1,3) and (-1,2). This means that option D is true.
