Read the text. People with asthma may experience difficulty breathing due to inflammation, or swelling, of the inner surfaces of their airways (the passageways by which air reaches the lungs). This inflammation makes the passageways sensitive to further irritation. Exposure to substances in the air such as pollen or smoke may then trigger an asthma attack. During an attack, the muscles around the airways contract, narrowing the space through which oxygen can pass. This can prevent oxygen from entering or exiting the lungs properly. Possible symptoms during an attack include shortness of breath, coughing, wheezing, and difficulty breathing. Which organizational structure does this text primarily use?
