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 of the following is a 'Protein Pump Inhibitor'? 
Select and explain. 
A. Ranitidine, B. Misoprostol, C. Omeprazole, D. Laxatidine
C: Omeprazole
Answer: C: Omeprazole 
Explanation: Omeprazole is a proton pump inhibitor, it inhibits gastric acid secretion. It inhibits the H+ K+ ATPase enzyme in the apical membrane of parietal cells, thereby reducing acid secretion. Acid secretion resumes only when new H+ K+ ATPase is formed. It is the treatment of choice for peptic ulcer, gastroesophageal reflux disease, and Zollinger Ellison syndrome. Ref: Essentials of Medical Pharmacology By KD Tripathi, 5th Edition, Page 589 - 94.