<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 45-year-old man with a 15-pack-year smoking history is referred for pulmonary function testing. On physical exam, he appears barrel-chested and mildly overweight, but breathes normally. Which of the following tests will most accurately measure his total lung capacity?? A: Spirometry, B: Open-circuit nitrogen washout, C: Body plethysmography, D: Closed-circuit helium dilution, E: Exhaled nitric oxide,  <response>: This question is asking about the most accurate test to measure total lung capacity in a patient with a history of smoking. The key details in the stem are the patients age, smoking history, barrel-chested appearance, and normal breathing on exam. Total lung capacity TLC refers to the total volume of air in the lungs after a maximal inhalation. To measure TLC accurately, we need a test that can assess total lung volumes rather than just airflow. Choice A spirometry measures airflow and forced vital capacity, not total volumes. Choice E exhaled nitric oxide is a measure of inflammation, not lung volumes. Choices B, C, and D nitrogen washout, body plethysmography, and helium dilution are all techniques that can measure total lung capacity. Of these, body plethysmography is considered the gold standard for measuring absolute lung volumes like TLC.C: Body plethysmography 