What is the function of a pronoun in a sentence?

The function of a pronoun in a sentence is to replace a noun, which is precisely why option B is the correct answer. Pronouns serve to avoid repetition of nouns, making sentences cleaner and more fluid. For example, instead of saying "Maria went to the store because Maria needed milk," one can say "Maria went to the store because she needed milk." Here, "she" is a pronoun that replaces "Maria," simplifying the sentence.

In contrast, the other options do not accurately describe the role of pronouns. Changing the subject of a sentence relates more to the grammatical function of subjects and verbs rather than the function of pronouns. Describing an action pertains to verbs, which convey what is happening in a sentence. Providing emphasis could involve certain types of pronouns, such as intensive pronouns, but this is not the primary or fundamental function of pronouns in general. Thus, the essence of a pronoun is indeed to serve as a replacement for nouns.