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
A 12-year-old girl has a history of recurrent bulky stools and abdominal pain since 3 years 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? 
Select and explain. 
A. Small intestinal biopsy, B. Barium studies, C. 24-hr- fecal fat estimation, D. Urinary d-xylose test
A: Small intestinal biopsy
Answer: A: Small intestinal biopsy 
Explanation: None