This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Malabsorbtion Syndrome, Subject name: Medicine
A 41 year old patient presented with chronic diarrhea for 3 months. A D-xylose absorption test was order to look for: 
Select and explain. 
A. Carbohydrate malabsorption due to mucosal disease, B. Carbohydrate malabsorption due to chronic pancreatitis, C. Fat malabsorption due to mucosal disease, D. Fat malabsorption due to chronic pancreatitis
A: Carbohydrate malabsorption due to mucosal disease
Answer: A: Carbohydrate malabsorption due to mucosal disease 
Explanation: 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. In cases of bacterial overgrowth, the values of D-Xylose absorption return to normal after treatment with antibiotics. In contrast, if the D-xylose urinary excretion is normal, then the problem must be due to a non-mucosal cause of malabsorption (i.e., pancreatic insufficiency).