This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Concept of health and disease, Subject name: Social & Preventive Medicine
[{'content': 'Iceberg phenomena is not seen in \nSelect and explain. \nA. Measles, B. AIDS, C. Polio, D. Rubella', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The only source of measles infection is case. Carriers are not know to occur. So, iceberg phonomena is not seen in measles. Ref : Park&;s Textbook of Preventive and Social Medicine; 23rd edition - Pgno 147', 'role': 'assistant'}]