B. The repetition of "Quoth the Raven 'Nevermore'."
Explanation:
The ghastly repetition of the phrase Nevermore in the poem by Edgar Allan Poe is able to derive on of the central themes of a poem. The raven represents a lot of things and in its prophetic voice coveys this central theme.
When the Raven says 'Nevermore' it means that never again will the poet be able to have the experience he is having right now as Gothic and supernatural as it is right now and this pang of grief that he is facing he will not be able to come to terms with.