The following factor affects the orbit of a satellite up to an altitude of 720 km from the earth's surface

Why: Up to about 720 km altitude, satellites are still in Low Earth Orbit (LEO), where the atmosphere is very thin but not absent. The residual air molecules produce aerodynamic drag on a satellite moving at roughly 7.5 km/s, which continuously removes orbital energy and causes gradual orbital decay.

Option A (Uneven gravitational field): Earth’s oblateness and mass irregularities do perturb orbits (e.g., nodal and apsidal precession), but at ~720 km these effects are secondary compared with drag when considering orbit maintenance and decay over practical timescales.

Option B (Gravity of the Sun and Moon): Third-body perturbations exist at all altitudes but are comparatively minor for LEO; their influence becomes relatively more important at higher altitudes (e.g., MEO/GEO).

Option C (Aerodynamic forces): Dominant disturbance in LEO up to ~720 km. Drag reduces velocity, lowers perigee, and accelerates decay, requiring periodic reboosts for orbit maintenance.

Conclusion: At altitudes up to 720 km, aerodynamic drag is the principal factor affecting a satellite’s orbit, making Option C correct.