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
Fever blisters can occur due to - 
Select and explain. 
A. HHV 6, B. Varicella, C. Primary HSV-1 infection, D. Reactivation of HSV-1
D: Reactivation of HSV-1
Answer: D: Reactivation of HSV-1 
Explanation: None