This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System Pa 1, Subject name: Physiology
[{'content': 'In a data collected from nitrogen wash-out method in a patient, volume of nitrogen was found to be 800 mL in his residual volume (RV). How much is the RV in this patient? \nSelect and explain. \nA. 400 mL, B. 800 mL, C. 1000 mL, D. 1600 mL', 'role': 'user'}, {'content': 'Answer: C \nExplanation: In all the respiratory volumes, 80% fraction is of nitrogen. Thus, if total nitrogen volume in the RV is 800 mL, then RV is 1000 mL. (80% of 1000 mL is 800 mL.)', 'role': 'assistant'}]