Which of the Following Best Describes the Chemical Principle of the Protein

Which of the following best describes the chemical principle of the protein reagent strip?

A) Protein reacts with an immune complex on the pad, which results in a color change.
B) Protein causes a pH change on the reagent strip pad that results in a color change.
C) Protein accepts hydrogen ions from an indicator dye, which results in a color change.
D) Protein causes protons to be released from a polyelectrolyte, resulting in a color change.