This is the 15112th most frequent Turkish word.
seçmesini
"Seçmesini" means "his/her/its choosing" or "the act of choosing."
Here, 'seçmesini' is used as a verbal noun form of 'seçmek' (to choose), expressing an expectation for someone else to choose.
Öğrencinin istediği konuyu seçmesini bekliyoruz.
We are waiting for the student to choose the topic they want.
Here, 'seçmesini' indicates the act of choosing a book, which is being evaluated or questioned.
Onun kitabı seçmesini anlamıyorum.
I don't understand their choice of the book.
Here, 'seçmesini' refers to delegating the action of choosing the best player, involving the infinitive in a possessive construction.