This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
[{'content': 'Severity of disease is assessed by: \nSelect and explain. \nA. Secondary attack rate, B. Case fatality rate, C. Prevalence rate, D. Incidence rate', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e. Case fatality rate Case fatality rate represents the killing power of the disease. It is closely related to virulence of the disease.", 'role': 'assistant'}]