<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 74-year-old woman with a past medical history of hypertension, peripheral artery disease, and migraine headaches presents to the emergency department with a two hour history of severe abdominal pain. The patient cannot recall any similar episodes, although she notes occasional abdominal discomfort after eating. She describes the pain as sharp periumbilcal pain. She denies recent illness, fever, chills, nausea, vomiting, or diarrhea. Her last normal bowel movement was yesterday evening. Her temperature is 37.1C 98.8F, pulse is 110min, blood pressure is 14080 mmHg, and respirations are 20min. On exam, the patient is grimacing and appears to be in significant discomfort. Heart and lung exams are within normal limits. The patients abdomen is soft and non-distended with diffuse periumbilical pain on palpation. There is no rebound tenderness or guarding, and bowel sounds are present. The rest of the exam is unremarkable. Labs in the emergency room show:Serum:Na: 144 mEqLCl-: 105 mEqLK: 3.7 mEqLHCO3-: 20 mEqLBUN: 15 mgdLGlucose: 99 mgdLCreatinine: 1.2 mgdLCa2: 10.7 mgdLPhosphorus: 5.2 mgdLLactate: 7.0 mmolLAmylase: 240 ULHemoglobin: 13.4 gdLHematocrit: 35Leukocyte count: 12,100 cellsmm3 with normal differentialPlatelet count: 405,000mm3What is the next best step in diagnosis?? A: D-dimer level, B: Plain abdominal radiograph, C: Exploratory laparotomy, D: CT angiography, E: Abdominal duplex ultrasound,  <response>: This is a question about diagnosing acute abdominal pain in an elderly woman with risk factors for vascular disease. Based on the history and physical exam findings of severe periumbilical pain without signs of peritonitis, mesenteric ischemia is a concern. The lab findings of an elevated lactate level also raise suspicion for bowel ischemia. The choices include tests for pulmonary embolism D-dimer, bowel obstruction plain film, exploratory surgery, CT angiography of the mesenteric vessels, and ultrasound of the abdominal vessels. CT angiography is the best next step to directly visualize the mesenteric vessels and assess for occlusion or stenosis causing the abdominal pain. Surgery and ultrasound are not definitive enough, while D-dimer and plain films will not provide information about the mesenteric vessels.D: CT angiography 