A 12-year-old girl has history of recurrent bulky stools and abdominal pain since 3 year of age. She has moderate pallor and her weight and height are below the 3rd percentile. Which of the following is the most appropriate investigation to make a specific diagnosis?

The given child has malabsorption syndrome associated with chronic diarrhea Intestinal biopsy is necessary to differentiate chronic diarrhea due to different pathophysiological reasons Iron absorption occurs from duodenum so, any disease involving duodenum will lead to anemia D-Xylose - monosaccharide, or simple sugar, that does not require enzymes for digestion prior to absorption. Its absorption requires an intact mucosa only. In normal individuals, a 25 g oral dose of D-xylose will be absorbed and excreted in the urine at approximately 4.5 g in 5 hours. A decreased urinary excretion of D-xylose is seen in small intestinal bacterial overgrowth and Whipple's disease.