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: Medicine
[{'content': 'Fever blisters can occur due to - \nSelect and explain. \nA. HHV 6, B. Varicella, C. Primary HSV-1 infection, D. Reactivation of HSV-1', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]