Explanation:

- Option 1: Castes are a term more commonly associated with the rigid social stratifications in India, not in 18th-century France.

- Option 2: Four Estates are not accurate for the French social structure of that period.

- Option 3: Three Estates refers to the way French society was divided in the 18th century—into the First Estate (clergy), Second Estate (nobility), and Third Estate (commoners).

- Option 4: Two Estates would not accurately reflect the three-part division that characterized French society at that time.