Which of the following is NOT a disease of the respiratory system?

Arthritis is not classified as a disease of the respiratory system. Instead, it is a condition that primarily affects the joints and surrounding tissues, leading to inflammation and pain. The respiratory system includes organs and structures involved in breathing, such as the lungs, bronchi, and trachea. Diseases like Chronic Obstructive Pulmonary Disease (COPD), bronchitis, and tuberculosis directly affect these components, leading to compromised respiratory function. COPD refers to a group of lung diseases that obstruct airflow and make breathing difficult. Bronchitis involves inflammation of the bronchial tubes, while tuberculosis is an infectious disease that primarily affects the lungs. Therefore, the only option that does not pertain to the respiratory system is arthritis.