<em>La alumna "PONE" los cuadernos en una mochila.</em>
Es su camiseta.
Su is used to show possession of singular objects, in this case, a t shirt, in third person form.
¿Puedo ir a estudiar a la biblioteca? When there are two verbs in succession, only the first should be conjugated. Puedo is first person singular present, so that is the correct answer.
