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
Which protease inhibtor has boosting effect ? 
Select and explain. 
A. Amprenavir, B. Tenofovir, C. Nelfinavir, D. Ritonavir
D: Ritonavir
Answer: D: Ritonavir 
Explanation: None