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
Which viral infection always causes clinical disease in human beings - 
Select and explain. 
A. Rubella, B. Poliomyelitis, C. Measles, D. Chicken pox
C: Measles
Answer: C: Measles 
Explanation: None