Which of the following refers to words used to replace nouns?

The correct answer is pronouns. Pronouns are a category of words specifically designed to take the place of nouns to avoid repetition and to simplify sentences. For example, instead of saying "Maria loves Maria's dog," one could say "Maria loves her dog," where "her" serves as the pronoun replacing "Maria's." This not only streamlines communication but also enhances clarity and flow in writing.

The other types of words mentioned serve different grammatical functions. Adjectives describe nouns and provide more detail about them, verbs express actions or states of being, and adverbs modify verbs, adjectives, or other adverbs to indicate how, when, where, or to what extent something occurs. Understanding these distinctions helps in recognizing the role each word plays in constructing sentences effectively.