Imagine if the earth is not inclined towards the plane of its orbit, then A. the circle of illumination will match with longitudinal lines. B. the circle of illumination will match with latitudinal lines. C. there will be no seasonal variation in a particular region. D. there will be more seasonal variation in a particular region.

Seasonal variations on Earth are caused by the tilt of Earth's axis (23.5°) relative to the plane of its orbit. If the Earth were not tilted, the circle of illumination (the line separating day from night) would pass through both poles and coincide with longitudinal (meridian) lines. Also, all parts of the Earth would receive sunlight in the same proportion throughout the year, so there would be no seasonal variation. Hence A and C are correct.