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
Proteins are separated on the basis of size by: 
Select and explain. 
A. SDS-PAGE, B. HPLC, C. Affinity Chromatography, D. Ion-exchange Chromatography
A: SDS-PAGE
Answer: A: SDS-PAGE 
Explanation: A i.e. SDS- PAGE