PRONOUNS: mine, yours, his, hers, its.'Possessive adjective' sits before a noun or a pronoun to show who or what owns it. The possessive adjectives are my, your, his, her, its, our, their, and WHOSE.'Adverb' is a word that modifies (DESCRIBES) a verb, an adjective, another adverb, or even a whole sentence.'Verb' is a word used to describe an action, state, or OCCURRENCE, and forming the main part of the predicate of a sentence.In the given sentence, the noun 'pen' belongs to someone. But his is used before a noun, therefore it is a possessive adjective.