Third person plural pronoun is THEY.
If you want to create a possessive pronoun out of that one, that would be THEIRS.
Possessive pronouns, as the name itself says, determine some kind of possession. For example:
Is this books yours? - No, it's theirs.
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Answer:
A.Justin walked through the gift shop, looking for a souvenir for himself.
Explanation:
Answer: Sayori, Yuri, Monika and Natsuki
Explanation: