What does an adjective modify?

An adjective modifies a noun, providing additional information about that noun's qualities, characteristics, or state. For example, in the phrase "the blue sky," the adjective "blue" describes the noun "sky," giving us more detail about what kind of sky it is. Adjectives help to paint a clearer picture in the reader's mind by specifying attributes such as color, size, amount, and other qualities.

When considering the other options, verbs, adverbs, and prepositions are modified by different parts of speech. For instance, adverbs modify verbs, telling us how, when, where, or to what degree something happens, while nouns are the primary focus of adjectives. This is why "a noun" is the correct answer, as it aligns with the role of adjectives in modifying and describing nouns.