Sound devices give lyric poetry its musical nature, that is, your answer would be D. They are resources used by poets to reinforce the meaning of the poetry. In poetry, the words and their order are supposed to evoke images and, as the words have sounds, they can make those images more clear in the readers' minds.
There are several sound devices a poet can resort to: alliteration, accent, assonance, consonance, cacophony, dissonance, euphony, internal rhyme, meter, among others.