UPSC CSE Prelims

Correct Option: D Explanation: Earth’s axis is tilted relative to its orbital plane; as Earth revolves around the Sun, each hemisphere receives seasonally changing daylight duration. Option-wise Analysis: A: Incorrect - Wrong: daily rotation causes ordinary day and night, not seasonal changes in their length. B: Incorrect - Wrong: orbital ellipticity is not the principal cause of seasonal day-length variation. C: Incorrect - Wrong: latitude controls the magnitude of variation but is not the changing seasonal mechanism. D: Correct - Correct: revolution combined with Earth’s tilted axis changes daylight duration across seasons.