You are answering a USMLE-style medical question. Question: A 32-year-old woman comes to the emergency department because a 5-week history of abdominal pain and bloody diarrhea that has worsened in the past 24 hours. She was diagnosed with ulcerative colitis 1 year ago but has had difficulty complying with her drug regimen. Her temperature is 38.2°C (100.8°F), pulse is 120/min, and blood pressure is 92/56 mm Hg. Examination shows a distended, rigid abdomen and hypoactive bowel sounds. Fluid resuscitation is initiated. In addition to complete bowel rest, which of the following is the most appropriate next step in management of this patient? Options: A) Abdominal CT scan with contrast B) CT angiography C) Abdominal x-ray D) Colonoscopy Reply with ONLY the letter of the correct answer (A, B, C, or D). No explanation.