Answer:
A). Adjective
Explanation:
Adverbs are elucidated as the words that function to modify a verb, adjective, other adverbs, or various other types of words, phrases, or clauses.
In the given sentence, the adjective 'boring' modifies the noun 'television show' and the adverb 'extremely' is modifying the adjective 'boring' by telling about the degree of intensity that how boring was the show. Thus, option A i.e. 'adjective' is the correct answer.
