Final answer:
An allegory's main purpose is to represent abstract ideas through concrete symbols, conveying deeper meaning, as seen in Plato's "Allegory of the Cave"; the correct option is (b).
Step-by-step explanation:
The main purpose of an allegory is to present abstract ideas through concrete symbols. This is not only to entertain the audience or to describe real-world events in a straightforward manner, or to provide factual information. Rather, an allegory uses characters, actions, and narrative elements as symbols to convey deeper, often moral or philosophical, truths about life.
A classic example of allegory is Plato's "Allegory of the Cave", where the author uses the story of prisoners in a cave to represent the journey from ignorance to enlightenment. The correct option for the main purpose of an allegory is therefore option (b).