Final answer:
Edgar Allan Poe often uses setting to establish the mood in his stories, with the environment and time reflecting the narrative's atmosphere and character development. Option a is correct.
Step-by-step explanation:
Among the elements Edgar Allan Poe uses to establish mood, the correct answer is a) Setting. Poe frequently employs setting as a critical factor in establishing the mood of his stories.
For instance, in "The Fall of the House of Usher", the somber, oppressive setting contributes significantly to creating a feeling of confinement and depression that resonates with the reader, highlighting the mood through the physical environment and time in which the story takes place. The setting in Poe's works often mirrors the internal development of characters as well, adding to the overall mood of the narrative.