Questions: The Meeting of St. Anthony and St. Paul painting signifies a long pilgrimage over time, rather than a single moment.

The answer is: series of episodes in one picture.

Explanation for each option:

1. Three visual clues telling us that the work portrays motion: This option is incorrect because the painting is not primarily about depicting motion through visual clues. Instead, it represents a narrative over time.

2. A basis for early attempts to show moving images: This option is incorrect because the painting is not related to the development of moving images or early cinema. It is a traditional artwork that tells a story through a series of scenes.

3. Series of episodes in one picture: This is the correct answer. The painting "The Meeting of St. Anthony and St. Paul" is known for depicting multiple episodes or scenes within a single frame, illustrating the journey and encounters of the saints over time.

4. Frames that were computer-generated using 3-D modeling software: This option is incorrect because the painting is a traditional artwork created long before the advent of computer-generated imagery and 3-D modeling software.