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
Gastro-intestinal enteritis necroticans caused by: 
Select and explain. 
A. CI difficile, B. CI. perfringens, C. Botulinum, D. C jejuni
B: CI. perfringens
Answer: B: CI. perfringens 
Explanation: “Necrotizing enteritis (enteritis necroticians, or pig bel) is caused by β toxin produced by type C strains of C.perfringens following ingestion of a high protein meal in conjunction with trypsin inhibitors by a susceptible host who has limited intestinal proteolytic activity”. Source of organism is patient own intestinal flora.
Clinical features

Acute abdominal pain, diarrhea, vomiting, shock and peritonitis, 40% of patient die.
Pathological studies shows an acute ulcerative process of the bowel restricted to small intestine.