This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Structure of proteins is best studied by: 
Select and explain. 
A. X -ray crystallography, B. Ultra centrifugation, C. Using Sangers reagent, D. Sucrose density gradient centrifugation
A: X -ray crystallography
Answer: A: X -ray crystallography 
Explanation: A Harper, 26th ed, p. 35 & 25th ed, p. 55