Passage Summary: Back when people thought Earth didn't move, they concluded stars had to be relatively close. Their logic was that if stars were far away, they'd have to move way too fast to get around the Earth in just 24 hours.

Conclusion: The stars were located no more than a few million miles away from Earth.

Reasoning: If Earth is stationary and the stars were further away, they would have to travel at impossibly high speeds to complete a circle around Earth every day.

Analysis: The argument relies on a 'gap' regarding physical limits. It assumes that there is a maximum speed at which stars can travel, or at least a speed that is 'too fast' to be plausible. If stars were capable of moving at any speed, regardless of how 'tremendously great' it was, the distance wouldn't be restricted by the 24-hour timeframe. To find the necessary assumption, look for a choice that suggests these high speeds are actually impossible or that the astronomers were operating under a specific speed limit for celestial bodies.