The time it takes for a planetary body to complete its orbit can be calculated using Kepler's Third Law of Planetary Motion, which primarily involves the mass of the sun and the radius of the orbit. However, when considering the options provided, the most relevant variable for this calculation is:
The radius of the orbit.
This is because Kepler's Third Law states that the square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit (which reflects the radius for circular orbits). While the mass of the sun determines the gravitational pull influencing the orbit, the radius is the primary factor used in the calculation of the orbital period.