So for graphs, to tell if its a function is to see how many points are on the x-line for the coordinate. Functions will only have one point on each x-line.
With the top left, x = 0 has 2 points on it, so that is incorrect.
With top right, x = -1 has 2 points on it, so its incorrect as well.
Bottom left has 3 points on x = 0, so that's incorrect.
Bottom right, however, has no x-line where there are two or more points on it, so it is a function.
