This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Cyclic trend is shown by- \nSelect and explain. \nA. Measles epidemic, B. Influenza pandemic, C. Rubella epidemic, D. All of the above', 'role': 'user'}, {'content': "Answer: D \nExplanation: Ans. is 'd' i.e., All of the above Cyclic trend* Some diseases occur in cyclic spread over a short period of time which may be week, days, months or years.* This is due to naturally occuring variation in herd immunity.* A build up of susceptible is again required in the herd before there can be another attack.* It may be due to antigenic variations as occur in influenza.* Examples - Epidemic of# Measles - every 2-3 years# Rubella - every 6-9 years# Pandemic of influenza - every 10-15 years.", 'role': 'assistant'}]