The vitamin riboflavin, which occurs as a yellow pigment in egg yolk and milk become

• A. colorless on oxidation and regained its color on reduction with Zn in acid
• B. colorless on reduction with Zn in acid and regained its color on re-oxidation
• C. more deep in color on oxidation and regained its color on reduction with Zn in acid
• D. more deep in color on reduction with Zn in acid and regained its color on re-oxidation