What is one way in which edgar allan poe creates a unity of effect of melancholy in the raven?

The correct answer is C.

Explanation:

In his poem, "The Raven," Poe achieves a unifies effect of melancholy through the repetition of the word "nevermore."

In the poem, the speaker is depressed by the loss of his lover, Lenore and  dreads that he will never see her again. This is why the word repeated by the raven causes so much pain and sadness in the speaker, and at the same time gives the poem an overall melancholly tone.