The correct option is A bronchioles
Asthma is a lung disease in which the bronchioles in the lungs swell and narrows down. The skin that lines the air passage swells and oozes out mucus. As a result, the person has difficulty in breathing. Generally two types of drugs are prescribed to asthma paitients: bronchodilators and steroids. Steroids act by reducing the degree of inflammation of the bronchioles.