This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Proteins can be separated by the following except 
Select and explain. 
A. Electrophoresis, B. Ultra - centrifugation, C. Gas chromatography, D. None
D: None
Answer: D: None 
Explanation: question repeated