Concept:Heat from the Sun reaches Earth through the vacuum of space, so it must travel by a method that needs no medium.Explanation:Conduction requires direct contact between particles to transfer heat.Convection requires a fluid (liquid or gas) to carry heat by movement.Space between the Sun and Earth is mostly empty, so neither conduction nor convection can occur.Radiation transfers heat by electromagnetic waves, which can travel through empty space.Therefore, only radiation carries the Sun's heat to Earth.Answer:C. III only.