This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
[{'content': 'Herd immunity is not seen in- \nSelect and explain. \nA. Poliomyelitis, B. Measles, C. Diphtheria, D. Tetanus', 'role': 'user'}, {'content': 'Answer: D \nExplanation: .', 'role': 'assistant'}]