Answer: D) sunless sea.
Step-by-step explanation: alliteration is a literary device that consists in the repetition of the beginning sound of consecutive words, or words that are close to each other in a sentence or paragraph, this repetition creates rhythm in the text. In the given excerpt from Samuel Taylor Coleridge’s “Kubla Khan” we can see an example of alliteration in the words "sunless sea" as we can see, the sound "s" is at the beginning of the two words.