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': 'Ventilation perfusion ratio is maximum at : \nSelect and explain. \nA. Apex of lung, B. Base of lung, C. Posterior lobe of lung, D. Middle of the lung', 'role': 'user'}, {'content': 'Answer: A \nExplanation: A i.e. Apex of lung', 'role': 'assistant'}]