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
In SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) proteins are separated on basis of: 
Select and explain. 
A. Mass, B. Charge, C. Density, D. None
A: Mass
Answer: A: Mass 
Explanation: A i.e. Mass