Which part of speech serves to replace a noun?

The correct answer is a pronoun because pronouns specifically function to replace nouns in order to avoid repetition and make sentences more fluid. Pronouns can refer to people, things, or concepts previously mentioned or easily identified in context, providing clarity and coherence in writing. Examples of pronouns include "he," "she," "it," "they," and "this," all of which serve to stand in for nouns, making them essential for effective communication.

In contrast, adjectives modify nouns by providing additional detail about their characteristics, but they do not replace them. Nouns are the part of speech that identify persons, places, things, or ideas rather than serving as substitutes. Adverbs modify verbs, adjectives, or other adverbs, yet they also lack the ability to replace nouns. Therefore, the role of a pronoun in language is unique and central to the structure of sentences, emphasizing its significance as the correct choice in this question.