This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Communicable diseases, Subject name: Social & Preventive Medicine
In an area not covered by measles immunization, the attack rate of measles is - 
Select and explain. 
A. 70%, B. 80%, C. 90%, D. 100%
C: 90%
Answer: C: 90% 
Explanation: when the disease is introduced to a virgin community more than 90 % of that community will be infected (park,edition 23,page 146)