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: Microbiology
Most common organism responsible for pseudo membranous colitis is ? 
Select and explain. 
A. Clostridium difficile, B. Clostridium botulism, C. Clostridium histolyticum, D. Clostridium butyricum
A: Clostridium difficile
Answer: A: Clostridium difficile 
Explanation: Ans. is 'a' i.e., Clostridium difficile