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': 'Surveillance is: \nSelect and explain. \nA. Scrutiny of factors, B. Treatment of contacts, C. Both, D. None of the abov', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Scrutiny of factors', 'role': 'assistant'}]