Answer:
Mr. Thompson is now accepting applications for his yearbook staff.
Step-by-step explanation:
Pronouns are words that replace nouns in sentences. Pronouns that express ownership are called possessive pronouns. They include pronouns my, mine, our, ours, its, his, her, hers, their, theirs, your and yours.
When we want to express something that belongs to a female, we say that something is her/hers. When something belongs to a male, it is his. In the given sentence, the subject is a man (Mr., or Mister Thompson), so the appropriate possessive pronoun is his: Mr. Thompson is now accepting applications for his yearbook staff. Had the subject been a female (e.g. Mrs. Thompson), the sentence would've been correct.