Answer:
her, his, their (sing)
Explanation:
This answer is based on (sing) meaning singular.
In Spanish "su" is used to show a singular person's possession. It is also in the third person; which in English correlates to he, she, they, etc. So, "su" can show possession for any singular, third-person pronoun. In this case, the fitting pronouns are her, his, and their (sing).
