The SDS in SDS-Polyacrylamide Gel Electrophoresis (SDS-PAGE) of a Protein

The SDS in SDS-polyacrylamide gel electrophoresis (SDS-PAGE) of a protein is used to

A) neutralize the charge of a protein so that charge is not a factor in its rate of migration.
B) denature the protein and give it an overall negative charge.
C) cross-link the protein's structure so that it does not become denatured during electrophoresis.
D) digest the protein into smaller fragments that are more easily separated by electrophoresis.