This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anti-Parasitic Drugs, 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: Metronidazole is the drug which is used to treat antibiotic associated pseudomembranous enterocolitis and is a component of anti H. pylori triple drug regimen. PSEUDO-MEMBRANE COLITIS MC organism responsible Clostridium difficile MC cause 3rd Gen. Cephalosporins > clindamycin DOC Metronidazole - Oral vancomycin According to latest guidelines, now oral vancomycin has become DOC for Pseudomembranous colitis.