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': 'Serial interval is the gap between- \nSelect and explain. \nA. Primary and secondary case, B. Index and primary case, C. Introduction of infection and development of maximum infectivity, D. Transmission infection from patient to another susceptible host', 'role': 'user'}, {'content': 'Answer: A \nExplanation: .serial interval is the time gap between the development of primary case and the fuher introduction of the disese agent into the community to cause secondary infections.from this we get a distribution of of secondary cases from which we can guess the incubation period of disease. ref:park&;s textbook,ed22,pg 95', 'role': 'assistant'}]