Step 1: Understand what causes seasons.
We need the real reason why Earth has summer, winter and other seasons.
Step 2: Earth's tilt.
Earth's axis is tilted by about $23.5^\circ$ compared to its path around the Sun. This tilt stays fixed as Earth moves.
Step 3: Effect of the tilt.
As Earth goes around the Sun, sometimes a hemisphere leans toward the Sun and gets more direct light. That gives summer. Later it leans away and gets weaker light. That gives winter.
Step 4: Why distance is not the reason.
Earth is actually closest to the Sun in early January, which is winter in the north. So distance cannot explain seasons.
Step 5: Why Sun's output and clouds are not the reason.
The Sun's energy stays nearly steady through the year. Clouds only change local weather, not the yearly season cycle.
Step 6: Conclude.
The tilt of Earth's axis, combined with its revolution, is the true cause of seasons.
Answer: Earth's axis is tilted relative to its orbit around the Sun