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': 'Aerial carbon dioxide level \nSelect and explain. \nA. 40 mm Hg, B. 37 mm Hg, C. 45 mm Hg, D. 60 mm Hg', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. 40 mmHg', 'role': 'assistant'}]