Answer:
D. The model cannot explain why planets appear to go backward and make loops in the sky.
Explanation:
As an example, the observation of the planet Mars shows that there are times where it seems to be moving forward at first, then back, and then forward again. If Earth were the center of the the universe, then everything would have been revolving in one direction. Although they tried to back up their theory by assuming that planets moved in their own epicycles, it was explained that Mars seems to be moving backwards because the Earth had a smaller orbit than Mars, so at times, it would pass Mars, which has not yet completed that section of the orbit. When Earth then completes its cycle around, it will find Mars again ahead of it, moving forward.
