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
. A useful index to measure the lethality of an acute infectious diseases is- 
Select and explain. 
A. Attack rate, B. Incidence rate, C. Case fatality rate, D. None of these
C: Case fatality rate
Answer: C: Case fatality rate 
Explanation: None