This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Central Nervous system, Subject name: Pharmacology
[{'content': 'Respiratory centre depression can be caused by all except \nSelect and explain. \nA. Opium, B. Strychnine, C. Barbiturates, D. Gelsemium', 'role': 'user'}, {'content': "Answer: B \nExplanation: Opium causes significant respiratory depression. Barbiturates does not produce respiratory depression. Strychnine doesn't produce respiratory depression , it is a convulsant. Ref: KD Tripathi 8th ed.", 'role': 'assistant'}]