Answer

C. Alliteration

Explanation

The type of figurative language being demonstrated in the sentence: "Polly's prancing pony performed perfectly" is called alliteration. Alliteration is defined as the occurrence of the same letter or sound at the beginning of several consecutive words in a sentence. In this sentence, the repetition of the initial 'p' sound in "Polly's", "prancing", "pony", "performed" and "perfectly" is an indication of the use of alliteration. A simile is a comparison using the words 'like' or 'as', which doesn't apply here. A metaphor involves an implicit comparison between two things that are not similar, hence doesn't apply here as well. Onomatopoeia, then, refers to the use words whose sound is suggestive of their meanings, but this phenomenon does not apply to the sentence above. Therefore, the phrase under examination clearly constitutes alliteration.