Which of the following is NOT one of Kepler's laws of planetary motion?

A. The orbit of each planet around the Sun is an ellipse with the Sun at one of the two foci.

B. The orbits of all planets around the Sun are coplanar.

C. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.

D. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.