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
Pseudomembranous colitis is associated mostly with which drug ? 
Select and explain. 
A. Erythromycin, B. Ampicillin, C. Vancomycin, D. Ciprofloxacin
B: Ampicillin
Answer: B: Ampicillin 
Explanation: None