Which relation is a function? 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. 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. Coordinate grid with graph of a vertical line at x equals 3. A coordinate grid containing a U shaped graph with arrows on its ends. The U shape opens upwards and the bottom of the U shape is located at the origin.