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: Medicine
[{'content': 'Respiratory centre depression is caused by all except- \nSelect and explain. \nA. Opium, B. Strychnine, C. Barbiturates, D. Gelsemium', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]