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': 'Regarding point sources epidemic, which is true? \nSelect and explain. \nA. Rapid rise and fall, B. Only infections cause, C. Explosive, D. Secondary attack rate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The main features The epidemic curve rises and falls rapidly with no secondary waves The epidemics tend to be explosive there is a clustering of disease within a narrow interval of time All cases develop within one incubation period (refer park pano:64 23rd edition)', 'role': 'assistant'}]