C

Step 1: In a planetary system, the motion of planets around the sun is governed by gravitational forces. Each planet moves in an orbit where the sun is at one of the foci of the elliptical path.
Step 2: The principle of conservation of angular momentum states that in the absence of external torques, the angular momentum of a system remains constant. In the case of the solar system, planets maintain their orbits without external torques acting on them, thus conserving angular momentum.
Step 3: As the planets move closer to the sun, they move faster to conserve angular momentum, and when they are farther away, they move slower.
Conclusion: Thus, the motion of the planets in the solar system illustrates the conservation of angular momentum.
Therefore, the correct answer is C.