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
[{'content': 'The substances present in the gall bladder stones or the kidney stones can be best identified by the following techniques - \nSelect and explain. \nA. Flourescence spectroscopy, B. Electron microscopy, C. Nuclear magnetic resonance, D. X - ray diffraction', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]