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
Measles epidemic can be anticipated when propoion of susceptible children in a community reaches - 
Select and explain. 
A. 20%, B. 40%, C. 60%, D. 80%
B: 40%
Answer: B: 40% 
Explanation: Measles tends to occurin epidemics when the propoion of susceptible children reaches about 40% Reference; Park&;s Textbook of preventive and social medicine, 24th edition.Pg no. 156