Final answer:
A. A conch shell
In the society formed by the boys in their story, a conch shell represents the symbol of authority, used for order and governance.
Step-by-step explanation:
The symbol of authority in the society that the boys form in their story is A. A conch shell. The conch shell is used to establish order, hold the power of speech during meetings, and summon the boys together. This object becomes a powerful symbol of civilization, governance, and authority among the boys stranded on the island. Such symbols in literature help convey deeper meanings and themes, much like how the American flag is a material object that denotes the U.S. and embodies nonmaterial culture concepts like bravery and freedom.