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: Medicine
Drug of choice for pseudomembranous colitis 
Select and explain. 
A. Penicillin, B. Metronidazole, C. Ciprofloxacin, D. Vancomycin
B: Metronidazole
Answer: B: Metronidazole 
Explanation: None