Final answer:
If Earth's spin axis were perpendicular to its orbital plane, we would experience no seasonal variation option(4), as the tilt of Earth's axis is what causes different parts of Earth to receive varying amounts of sunlight throughout the year.
Step-by-step explanation:
If Earth's spin axis were perpendicular to Earth's orbital plane (the ecliptic plane), then the seasons and seasonal variation would be nonexistent. The axial tilt of the Earth is responsible for the different seasons because it affects the intensity and concentration of the Sun's energy received by different parts of the planet throughout its orbit.
Without this tilt, every place on Earth would experience the same duration of daylight and temperature year-round; consequently, seasonal changes would not occur.
Currently, due to the 23.5° tilt of Earth's axis, different latitudes receive varying amounts of sunlight at different times of the year, leading to temperature shifts and our well-known seasonal cycle. However, if Earth had no tilt, the Sun's path in the sky would remain the same each day across the year, with no change in the angle or intensity of sunlight to drive temperature shifts.
Thus, the hypothesis that Earth's changing distance from the Sun causes seasons is incorrect. It's the tilt of the Earth's axis which creates the varying conditions that result in seasonal weather patterns. In summary, a perpendicular spin axis to the ecliptic plane would mean that Earth's environment would be in a persistent equinox-like state.