When Performing 2-D Gel Electrophoresis, What Is the Purpose of Exposing

When performing 2-D gel electrophoresis, what is the purpose of exposing the proteins to sodium dodecyl sulfate (SDS) ?

A) SDS masks all of the proteins' native charge with a positive charge.
B) SDS masks all of the proteins' native charge with a negative charge.
C) SDS makes all of the proteins' the same molecular weight.
D) SDS adds a hydroxyl group to amino acid residues on each of the proteins.
E) SDS masks all of the proteins' native charge with a neutral charge.