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
Structure of proteins can be detected by all the methods, EXCEPT: 
Select and explain. 
A. High pressure liquid chromatography (HPLC), B. Mass spectrometry, C. NMR spectrometry, D. All of the above
A: High pressure liquid chromatography (HPLC)
Answer: A: High pressure liquid chromatography (HPLC) 
Explanation: High-performance/pressure liquid chromatography (HPLC) is a technique used for enhanced and precise separation of even small amounts of biological and nonbiological molecules. HPLC columns utilize variations of the separation principle behind column chromatography, depending on variable attractive and repulsive forces on the gel material and their interaction with the biological molecules. The analysis of peptides and structure of proteins are done by mass spectrometry. NMR spectroscopy analyzes proteins in aqueous solution. Proteins and protein complexes of >100 kDa can be analyzed by NMR. Ref: Janson L.W., Tischler M.E. (2012). Appendix II. Biochemical Methods. In L.W. Janson, M.E. Tischler (Eds), The Big Picture: Medical Biochemistry.