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
Select the drug which is used to treat antibiotic associated pseudomembranous enterocolitis and is a component of anti H. pylori triple drug regimen : 
Select and explain. 
A. Amoxicillin, B. Vancomycin, C. Metronidazole, D. Clotrimazole
C: Metronidazole
Answer: C: Metronidazole 
Explanation: None