<prompt>  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 16096 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 diagnosis -Idiopathic ulcerative colitisBacillary dysenteryIschaemic colitisAmoebic colitis 