Any graph will represent a function if it passes the vertical line test. A graph is a function if for any vertical line drawn it touches the graph at only one point.In other words for every x there is only one y value.
In the given graphs if a vertical line is drawn in the graphs A,B it will touch the graph at two points and hence they are not unctions.Option c s a vertical line that is for one x value there are more than one value of y and so is not a function.Option D will represent a function as any vertical line drawn will touch the graph at only one point.
OPtion D.
