This is the 50th most frequent Norwegian word.
sine
"Sine" is a Norwegian possessive pronoun meaning "his," "her," "its," or "their" (reflecting ownership by the subject of the sentence in plural or definite forms).
Here, 'sine' is a possessive pronoun used to indicate that the gloves belong to the subject, 'hun' (she).
Hun tok på sine hansker før hun gikk ut.
She put on her gloves before she went out.
In this context, 'sine' is a possessive pronoun that matches 'elevene' (the students), indicating the books belong to them.
Elevene har alltid med seg sine bøker til timene.
The students always bring their books to class.
Here, 'sine' denotes possession, relating the keys to the subject, 'han' (he), and corresponds to the plural noun 'nøkler' (keys).