The correct answer is:
a A combination of the forward motion of the objects and the pulling force of gravity create the rounded orbit shapes.
Newton's Law of Universal Gravitation explains that every mass attracts every other mass with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This gravitational force pulls celestial objects towards each other, while their forward motion (inertia) causes them to continue moving in a straight path. The balance between these two forces results in elliptical orbits, as described by Kepler's laws of planetary motion.