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: Social & Preventive Medicine
[{'content': 'Following is a contact poison – \nSelect and explain. \nA. BHC, B. BaSO4, C. A + B of above, D. Paris green', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]