The correct answer is a refrain.
"The Raven" is a narrative poem written by Edgar Allan Poe in 1845.
Throughout the poem, Poe uses the word nevermore many times. He makes use of the raven to utter this word. The raven said this every time the man asks a question.
By definition, a refrain is a line,phrase or set of lines that are repeated in a poem. The reader usually encounters these at the end of the stanza.