Answer: The graph that represents a function is the parabola that opens to the left.
This can be determined by the following characteristics of the graph:
It is a parabola because it opens to the left and has a vertex on the y-axis.
It crosses the y-axis at (0, 3) and (0, negative 3), which means that it is symmetric about the y-axis, and also it crosses the x-axis at (9, 0) which means that it is a function.
A circle is not a function because, for any value of x, there are two different values of y that can be plotted on the graph (i.e. the point (5,0) and (-5,0) produce two different y values)
A straight line with a positive slope is not a function because, for any value of x, there is only one value of y that can be plotted on the graph.
So the parabola is the graph that represents a function.
Explanation: