c. Retrograde motion of the planets as they moved across the sky.
Explanation:
Ancient Greek philosophers were extremely intelligent people who propounded some ideas that have helped shape science to what it is today.
They had evidence for the spherical shape of the earth, the link between lunar phases and oceanic tides, and the existence of exoplanets, however, they did not have evidence for the retrograde motion of the planets as they moved across the sky because they believed that if the Earth moved around the Sun, then they would be able to see the stars from divergent points along Earth's orbit.
