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: Biochemistry
The substance present in the gall bladder stones or the kidney stones can be best identified by the following techniques: 
Select and explain. 
A. Fluorescence spectroscopy, B. Electron microscopy, C. Nuclear magnetic resonance, D. X-ray diffraction
D: X-ray diffraction
Answer: D: X-ray diffraction 
Explanation: Polarizing microscopy, X-ray diffraction and infrared spectroscopy are techniques for analysing renal and gall bladder stones.