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': '. Herd immunity is not useful in - \nSelect and explain. \nA. Diphtheria, B. Tetanus, C. Small pox, D. Mumps', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]