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: Medicine
[{'content': 'Sentinel surveillance is done for: September 2003 \nSelect and explain. \nA. Missed cases, B. Subclinical case, C. Index cases, D. Prodromal infection cases', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A i.e. Missed cases', 'role': 'assistant'}]