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': 'The fraction of O2 in inspired air in mouth-to-mouth respiration is \nSelect and explain. \nA. 0.16, B. 0.19, C. 0.21, D. 0.26', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The concentration of O2 in the expired air is 16%. That air is is transferred by mouth to mouth respiration.', 'role': 'assistant'}]