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
The drug causing pseudomembranous colitis: 
Select and explain. 
A. Clindamycin, B. Clindamycin, C. Vancomycin, D. Penicillin
A: Clindamycin
Answer: A: Clindamycin 
Explanation: Clindamycin