This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
[{'content': 'Which of the following is true about Residual volume? \nSelect and explain. \nA. Is a pa of the expiratory reserve volume, B. Is a pa of vital capacity, C. Cannot be measured directly with a spirometer, D. Represents the resting volume of the lungs', 'role': 'user'}, {'content': 'Answer: C \nExplanation: The volume of air remaining in the lungs after a maximal effo to exhale all the air possible (ie, after your best effo to "empty" your lungs) is the residual volume. This volume cannot be measured directly by a spirometer, which measures only change in volume. Since you cannot voluntarily change your lung volume below the residual volume, the spirometer cannot measure it. Other methods (eg, body plethysmography, ine gas dilution) must be used to measure residual volume.', 'role': 'assistant'}]