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': 'Secondary attack rate (SAR) denominator includes \nSelect and explain. \nA. Population, B. Primary case, C. Exposed susceptible contacts, D. Person developing symptoms', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]