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
[{'content': 'All of the following drugs are protease inhibitors, EXCEPT: \nSelect and explain. \nA. Nelfinavir, B. Saquinavir, C. Abacavir, D. Ritonavir', 'role': 'user'}, {'content': "Answer: C \nExplanation: Abacavir is nucleoside reverse transcriptase inhibitor and not a protease inhibitor. Nelfinovir, Titonavir and Saquinavir are all protease inhibitor. Ref: Antiretroviral Therapy By Erik De Clercq, 2001, Page 147 ; Harrison's Principles of Internal Medicine, Pages 1124, 1126.", 'role': 'assistant'}]