They do that because it may not be said normally, it may have an accent attached along with it.
Answer:
The correct answer is: su/sus
Explanation:
In Spanish, we can use the following structure to express the possession of a certain thing: <u>object + de + person</u>.
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
Mi maestro pensó
Mi maestro y yo preferimos
Los estudiantes no mienten
Juanito pide
Yo defendi
