This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
Which is the following the test of choice for assessment of mucosal function of GIT? 
Select and explain. 
A. Biopsy, B. Schilling test, C. D-xylose test, D. Small bowel study
C: D-xylose test
Answer: C: D-xylose test 
Explanation: D-Xylose is a carbohydrate which is normally absorbed from the small intestine. Measuring D-xylose level in the serum or its excretion in urine after ingestion, is used for the evaluation of carbohydrate absorption ability of the proximal small intestinal mucosa. Ref: Pocket Guide to Diagnostic Tests By Diana Nicoll, 5th Edition