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': "In T.B. a 'case' is: \nSelect and explain. \nA. Cough, B. Sputum positive, C. Mantoux positive, D. X-ray positive", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Sputum positive', 'role': 'assistant'}]