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': 'In epidemic, 1st step is - \nSelect and explain. \nA. Verification of diagnosis, B. Isolation, C. Immunization, D. Notification', 'role': 'user'}, {'content': "Answer: A \nExplanation: Investigation of an epidemic: Verification of diagnosis Confirmation of the existence of an epidemic Defining the population at risk Rapid search for all cases and their characteristics Data analysis Formulation of hypothesis Testing of hypothesis Evaluation of ecological factor Fuher investigation of population at risk Writing the repo Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 143", 'role': 'assistant'}]