This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
[{'content': 'Vaccine which is eradicated worldwide is - \nSelect and explain. \nA. Small pox, B. Polio, C. Measles, D. Diphtheria', 'role': 'user'}, {'content': "Answer: A \nExplanation: Small pox is eradicated worldwide, so no vaccine. REF. PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICAL 21ST EDITION. PAGE NO - 132", 'role': 'assistant'}]