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
A 60 years old man presents with acute onset of pain in lower abdomen followed by repeated rectal bledding Examination revealed pulse rate of 100/ minute, BP 160/96 mm of Hg and a localised tenderness in the left hypochondrium. Stools examination reveales only a few pus cells and sigmoidoscopy was normal. Which one of the following is the most likely diagnos - 
Select and explain. 
A. Idiopathic ulcerative colitis, B. Bacillary dysentery, C. Ischaemic colitis, D. Amoebic colitis
C: Ischaemic colitis
Answer: C: Ischaemic colitis 
Explanation: Ans. is 'c' i.e., Ischaemic colitis