The correct option is D Flavoprotein
A conjugated protein is a protein to which another nonprotein group (a prosthetic group), such as a carbohydrate, lipid group etc., is attached. Some examples of conjugated proteins are lipoproteins, glycoproteins, phosphoproteins, hemoproteins, flavoproteins, metalloproteins, phytochromes, cytochromes and opsins. In flavoproteins, the nonprotein part is the flavin molecule which is a derivative of riboflavin. Thus, the correct answer is D.