<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:An institutionalized 65-year-old man is brought to the emergency department because of abdominal pain and distension for 12 hours. The pain was acute in onset and is a cramping-type pain associated with nausea, vomiting, and constipation. He has a history of chronic constipation and has used laxatives for years. There is no history of inflammatory bowel disease in his family. He has not been hospitalized recently. There is no recent history of weight loss or change in bowel habits. On physical examination, the patient appears ill. The abdomen is distended with tenderness mainly in the left lower quadrant and is tympanic on percussion. The blood pressure is 11079 mm Hg, heart rate is 100min, the respiratory rate is 20min, and the temperature is 37.2C 99.0F. The CBC shows an elevated white blood cell count. The plain abdominal X-ray is shown in the accompanying image. What is the most likely cause of his condition?? A: Acute diverticulitis, B: Toxic megacolon, C: Sigmoid volvulus, D: Intussusception, E: Colon cancer,  <response>: Based on the information provided in the question stem, the patient is a 65-year-old man with acute onset of abdominal pain, distension, nausea, vomiting and constipation. He has a history of chronic constipation and laxative use. There is tenderness mainly in the left lower quadrant and tympanic abdomen on exam. Lab tests show an elevated white blood cell count. The abdominal X-ray shows a dilated loop of large bowel in the left lower quadrant with an air-fluid level. This presentation is most consistent with sigmoid volvulus. Sigmoid volvulus commonly presents with sudden onset of abdominal pain, distension, constipation and vomiting. The plain film finding of a dilated loop of sigmoid colon with an air-fluid level is classic for this diagnosis. The other options can be ruled out based on details provided. Acute diverticulitis would cause left lower quadrant pain but no bowel dilation on X-ray. Toxic megacolon and intussusception are less likely in an elderly patient with no prior colon disease. Colon cancer could cause obstruction but not the sudden onset of symptoms seen here.C: Sigmoid volvulus 