Answer:
The correct answer is: su/sus
Explanation:
In Spanish, we can use the following structure to express the possession of a certain thing: object + de + person.
e.g. el libro de Juan
We also can replace the name of the person (3rd person of the singular) with a possessive adjective (su or sus).
e.g. su libro
We use the possessive adjectives to express who possesses something.
For plural forms, we use possessive adjective form - sus.
e.g. los libros de Juan y Ana = sus libros
