The correct answer is c. His shirt was extremely tight. An adverb is a describing word (often ending in -ly, but not always) that modifies verbs, adjectives, and other adverbs. An adjective is a describing word that modifies nouns. In the sentence "His shirt was extremely tight," the adverb "extremely" is modifying the adjective "tight," which is modifying the noun "shirt." In all the other options, the adverbs are modifying the verbs rather than adjectives.
