What identifies a person, place, or thing in a sentence?

Identifying a person, place, or thing in a sentence is the primary function of a noun. Nouns serve as the building blocks of sentences, providing the names for specific entities such as individuals (like "teacher"), locations (like "park"), or objects (like "book"). This definition clearly aligns with the purpose of nouns, making them essential for conveying information about the subjects of sentences.

In contrast, other parts of speech play different roles. Adverbs modify verbs, adjectives, or other adverbs but do not identify entities. Verbs indicate actions or states of being but do not specifically name things. Pronouns replace nouns to avoid repetition (e.g., "he" for "the teacher"), but they still represent nouns rather than identify new persons, places, or things directly. Therefore, the correct answer is indeed the noun, as it specifically fulfills the function of identifying individuals, locations, and objects in a sentence.