Which is the most important therapeutic approach to promote pulmonary function for the client with cystic fibrosis?

A. Corticosteroids are not a routine treatment for CF pulmonary function. B. Continuous oxygen therapy is not the primary intervention in CF unless advanced disease necessitates it. C. Antibiotics are essential for infection management, but not the main therapeutic approach for pulmonary function. D. Chest physiotherapy helps in mobilizing and clearing thick mucus from the lungs, a critical aspect of managing cystic fibrosis.