Final answer:
In 'The Alchemist', one attacker tells Santiago a legend of the oasis as they meet in the desert.
Step-by-step explanation:
The story that one attacker tells Santiago is B) A legend of the oasis. In the book 'The Alchemist' by Paulo Coelho, Santiago meets a group of attackers in the desert who initially threaten him, but then share a story about an oasis where one can find great treasure. This story plays a significant role in Santiago's journey and quest for his personal legend.