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: Dental
[{'content': 'All of the following are true regarding point source epidemic except _____. \nSelect and explain. \nA. No secondary waves., B. Clustering of cases within a short period of time., C. Only due to an infectious agent., D. All cases usually develop within one incubation period.', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Point source epidemics:\n\nBelong to common source type of epidemics.\nAlso called single exposure epidemics.\nAll cases develop within one incubation period.\nIn epidemic curve, there is sharp rise and fall as all cases are clustered within one incubation period and there are no secondary waves.\xa0\xa0\nNot only infectious agents but , environmental pollution and contamination of food can also cause point epidemics', 'role': 'assistant'}]