Which relation is a function? Coordinate grid with graph of a vertical line at x equals 3. A coordinate grid with graph of a curve that increases through the third quadrant through the origin and exits the first quadrant A coordinate grid with the graph of a circle centered at the origin and passing through the point begin ordered pair 2 comma 1 end ordered pair. A coordinate grid containing a U shape with arrows on both ends that opens to the right. The bottom portion of the U passes through the origin.