Which of the following is not a function of the upper respiratory tract?

The upper respiratory tract includes the nose and nasal passages, paranasal sinuses, the pharynx, and the portion of the larynx above the vocal folds. The lower  respiratory tract includes the portion of the larynx below the vocal folds, trachea, bronchi and bronchioles. Exchange of gases occurs in the exchange zone (respiratory bronchioles, alveolar ducts and alveoli) of the lower respiratory tract. The nose is a part of the conducting zone and performs all the other three functions.