Why is the work done by the gravitational force on a comet, which moves around the sun in highly elliptical orbits where the gravitational force is not normal to the comet's velocity, zero over every complete orbit?

Options

1. AThe gravitational force on the comet is always perpendicular to its velocity.
2. BThe comet's velocity remains constant throughout its orbit.
3. CThe work done by the gravitational force is canceled out by the kinetic energy of the comet.
4. DThe work done by the gravitational force is compensated by the potential energy changes in the comet-sun syste