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. Reactivation of HSV - 1, B. Primary HSV — 1 infection, C. Varicella, D. HHV- 6', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]