Many of the planets in the solar system have orbits of similar shapes, but they orbit at very different speeds. Why do the planets orbit at different speeds?

Question

A.
Planets are kept in their orbits by tension force, which is affected by the atmospheric pressure of a planet.

B.
Planets are kept in their orbits by electromagnetic force, which is affected by the diameter of a planet.

C.
Planets are kept in their orbits by friction, which is affected by the temperature of a planet.

D.
Planets are kept in their orbits by gravity, which is affected by the mass of a planet.

Answer 1

D.
Planets are kept in their orbits by gravity, which is affected by the mass of a planet.