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: Pathology
[{'content': 'Minimum dose of tetracycline which causes discoloration of teeth: \nSelect and explain. \nA. 10mg/kg Body weight., B. 20mg/kg Body weight., C. 30mg/kg Body weight., D. 40mg/kg Body weight.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]