Which sentence discusses the medium of its subject?
A. Fantasy stories often involve animals and supernatural figures that don't exist in the real world.
B. The theater group Elevator Repair Service is famous for Gatz, a play based on the novel The Great Gatsby.
C. I prefer reading adventure stories to romances.
D. In the novel Ash, a modern retelling of Cinderella, a young woman must live with her evil stepmother.