The correct response for understanding Kepler's third law of motion is:
orbital velocity, distance to sun
Kepler's third law states that the square of the period of revolution (the time it takes for a planet to orbit the sun) is proportional to the cube of the semi-major axis of its orbit (the average distance from the sun). So, the variables involved primarily relate to the period of revolution and the distance (semi-major axis) from the sun.