Answer:
Onomatopoeia is the correct answer.
Explanation:
An onomatopoeia is a word that tries to imitate the natural sound of something, in this case, how the hippos grunt. In the excerpt, we can see strong consonants together, such as "r", "p", and "t" sounds very close, trying to imitate the sound a hippo produce. It is necessary to remark that even there are synonyms (like snort) the effect on the reader might be different.
Assonance refers to the repetition of a vowel sound in different words that are close.
Alliteration is a device in which some words with the same consonant sound (at the beginning) are put together.
Rhyme is the similar sound between two words or their corresponding endings, usually at the end of a line in poetry.
