B
(In asthma, spasm of the smooth muscle of the bronchi and bronchioles causes constriction, producing impaired respiratory function. Atopy, or development of an immunoglobulin E (IgE)mediated response, is inherited but is not the only cause of asthma. Asthma is characterized by increased resistance in the airway. Asthma has multiple causes, including allergens, irritants, exercise, cold air, infections, medications, medical conditions, and endocrine factors.)