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': 'Which of the following is a characteristic of a point source epidemic? \nSelect and explain. \nA. Herd immunity regulates spread of cases, B. Person to person transmission is seen, C. Secondary waves of cases is always seen, D. All cases develop within one incubation period', 'role': 'user'}, {'content': "Answer: D \nExplanation: .point source epidemics ,here the period of exposure is only brief,and simultaneous ,the resultant cases will develop within one incubation period of the disease.the curve has usually one peak.the epidemic curve rises and falls rapidly, with no secondary waves.and it tends to be explosive. ref:park's textbook,ed 22,pg no 62", 'role': 'assistant'}]