Which of the following statements about SDS polyacrylamide gel electrophoresis is correct?

A、Wanted proteins can be tested for their biological activity after separation by SDS polyacrylamide gel electrophoresis.;

B、Proteins are solubilized but not denatured when separated by SDS polyacrylamide gel electrophoresis.;

C、SDS polyacrylamide gel electrophoresis separates proteins on the basis of size.;

D、SDS polyacrylamide gel electrophoresis separates proteins on the basis of charge.