The best explanation for why the Southern Hemisphere experiences seasons opposite to those in the Northern Hemisphere is that the tilt of Earth's axis results in different areas receiving varying amounts of direct sunlight throughout the year. However, none of the provided responses accurately captures this explanation.
The correct reasoning is that the Earth's axial tilt remains consistent in the same direction during its orbit, causing the Southern Hemisphere to experience summer when the Northern Hemisphere experiences winter and vice versa.
If you must choose from the provided responses, the closest (though still incorrect) would be "The Southern Hemisphere receives less direct sunlight during its summer," but it's important to note that the key reason is the axial tilt rather than a reversal or changes in distance to the sun.