This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other Key Definitions & Concepts, Subject name: Social & Preventive Medicine
[{'content': 'Secondary attack rate reflects ------ of a disease:- \nSelect and explain. \nA. Severity, B. Communicability, C. Fatality, D. Virulence', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Secondary attack rate = Primary case is excluded from both the numerator and denominator. It determines the communicability of the disease.', 'role': 'assistant'}]