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: Pharmacology
All are protease inhibitor EXCEPT : 
Select and explain. 
A. Ritonavir, B. Amprenavir, C. Tenofovir, D. Nelfinavir
C: Tenofovir
Answer: C: Tenofovir 
Explanation: None