This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy, Subject name: Pharmacology
All of the following drugs are protease inhibitors EXCEPT: 
Select and explain. 
A. Nelfinavir, B. Saquinavir, C. Abacavir, D. Ritonavir
C: Abacavir
Answer: C: Abacavir 
Explanation: ANTIVIRAL DRUGS: CLASSI FICATION 1.Anti-Herpes virus Idoxuridine, Acyclovir, Valacyclovir, Famciclovir, Ganciclovir*, Foscarnet* 2 Anti-Retrovirus (a) Nucleoside reverse transcriptase inhibitors (Nis): Zidovudine (AZT), Didanosine, Zalcitabine*, Stavudine, Lamivudine, Abacavir (b) Nonnucleoside reverse transcriptase inhibitors (NNis): Nevirapine, Eirenz, Delavirdine* (c) Protease inhibitors: Ritonavir, Indinavir, Nelfinavir, Saquinavir, Amprenavir*, Lopinavir 3. Anti-Influenza virus Amantadine, Rimantadine* 4. Nonselective antiviral drugs Ribavirin, Lamivudine, Adefovir dipivoxil, Interferon alpha. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:767