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: Surgery
Pseudomembranous colitis is caused by 
Select and explain. 
A. Cl. perfringens, B. Cl. difficile, C. Cl. oedematicus, D. Si. septicum
B: Cl. difficile
Answer: B: Cl. difficile 
Explanation: None