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
[{'content': 'A 56 year old woman has not passed stools for the last 14 days. Xray shows no air fluid levels. Probable diagnosis is : \nSelect and explain. \nA. Paralytic ileus, B. Aganglionosis of the colon, C. Intestinal pseudo-obstruction, D. Duodenal obstruction', 'role': 'user'}, {'content': "Answer: C \nExplanation: Air fluid levels are unusual in intestinal pseudoobstruction and should raise the possibility of mechanical obstruction. Ref: Harrison's Internal Medicine, 14th Edition, Page 1650 and 15th Edition, Page 1697; Update Gastroenterology 2004: New Developments in the Management of Benign gastrointestinal Disorders, 2004, Page 103.", 'role': 'assistant'}]