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
[{'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: None', 'role': 'assistant'}]