The correct option is "Some words that are usually nouns can function as adjectives."
Explanation:
Sometimes nouns are used to modify other nouns. In that case, nouns function as adjectives. For example, the word "science" is a noun but if we use it as "science teacher" then it acts as and adjective modifying the word "teacher".
The rest of the options are incorrect since the adjective only modifies a noun and adverbs can modify verbs, adjectives and other adverbs.
