What is an appropriate diagnostic study for abdominal pain described as distended, bloated, that is improved after flatulence possibly related to large bowel obstruction?

Rationale: A. Used to visualize the upper gastrointestinal tract (esophagus, stomach, duodenum). It does not provide information about bowel obstruction in the large intestine. B. Allows direct visualization of the colon mucosa but is not typically used initially in suspected acute bowel obstruction due to the risk of perforation. C. Useful for evaluating gallbladder, liver, kidneys, and sometimes bowel, but it is less sensitive for detecting large bowel obstruction. D. A plain abdominal X-ray (KUB) is often the first-line diagnostic study for suspected large bowel obstruction. It can show dilated bowel loops, air-fluid levels, and fecal loading, which correlate with the patient’s symptoms of bloating, distention, and relief after flatulence.