This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Physiology
[{'content': 'CO2 retention is seen in \nSelect and explain. \nA. Carbon monoxide poisoning, B. Respiratory failure, C. High altitude, D. Ventilatory failure', 'role': 'user'}, {'content': 'Answer: D \nExplanation: CO2 retention seen in ventilatory failure Ref: guyton and hall textbook of medical physiology 12 edition', 'role': 'assistant'}]