The correct answer is A. It includes alliteration, imagery, and a simile.
Alliteration is the repetition of the same consonant in neighboring words - as you can see, the consonant H is repeated in helmeted and heads. Imagery is achieved when descriptive vocabulary is used so that you can imagine a vivid picture just by reading those words, which is the case in this sentence. Simile is comparison using words such as like or as - in this sentence, the simile is '...bobbed like jellyfish...'
