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
[{'content': 'Which viral infection always causes clinical disease in human beings- \nSelect and explain. \nA. Rubella, B. Poliomyelitis, C. Measles, D. Chicken pox', 'role': 'user'}, {'content': "Answer: C \nExplanation: Rubella unfections are in fact subclinical.This represents the one of the major difference between measles and rubella(Ref.PARK'S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE 21st Edition page no.136)", 'role': 'assistant'}]