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: Social & Preventive Medicine
[{'content': 'The area is declared free of epidemic \nSelect and explain. \nA. No new case reported for twice the incubation period of disease since the last case, B. No new case reported for the incubation period of disease since the last case, C. Till last secondary case recovers, D. No new case reported for six months since the last case', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Investigation of an Epidemic:\n– To define magnitude or involvement (time, place, person)\n– To determine responsible conditions and factors\n– To identify causes, source(s) and modes of transmission\n– To make recommendations to prevent reoccurrence.', 'role': 'assistant'}]