The phrase 'haven under the hill' is an example of—

The phrase 'haven under the hill' repeats the consonant sound 'h' at the beginning of three closely placed words—haven, under (vowel), hill. Specifically, 'haven' and 'hill' both begin with the same 'h' sound, exemplifying alliteration—the repetition of initial consonant sounds in neighboring words. Hence (3) alliteration is correct.