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: Surgery
The substances present in the gall bladder stones or the kidney stones can be best identified by the following techniques - 
Select and explain. 
A. Flourescence spectroscopy, B. Electron microscopy, C. Nuclear magnetic resonance, D. X - ray diffraction
D: X - ray diffraction
Answer: D: X - ray diffraction 
Explanation: None