Retrograde Motion Was a Major Source of Difficulty in Designing

Multiple Choice

Retrograde motion was a major source of difficulty in designing a theoretical model of the solar system. What is the explanation for retrograde motion?

A) The planets actually stop and reverse direction in their orbits.
B) The planets move not in uniform circular motion about the Sun but rather in circular orbits (epicycles) about points which themselves move about the Sun in circular orbits.
C) Retrograde motion is an apparent motion of other planets, which we observe only because we are viewing their motion from Earth, itself in motion around the Sun.
D) Retrograde motion is an apparent motion caused by the precession of Earth's rotation axis.