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
. Herd immunity is not useful in - 
Select and explain. 
A. Diphtheria, B. Tetanus, C. Small pox, D. Mumps
B: Tetanus
Answer: B: Tetanus 
Explanation: None