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': 'Cardiac index ratio is determined by \nSelect and explain. \nA. CO & surface area, B. Stroke Volume & surface area, C. Surface area only, D. Peripheral resistance', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]