It's not an adverb, I seen it on the question I missed on Edgenuity. Teacher told me that it's not an adverb, but is is a noun. So the correct answer would be A: Noun
Explanation: In a sonnet, a two line stanza is typically referred to couplet...and it's usually structurally at the ending of the poem...in the case of a fourteen line poem (sonnet).