The correct option is D Keratin
The human skin is made up of multiple layers of ectodermal tissue which guards the underlying organs, muscles and ligaments. being similar to all mammals, these are covered by hair follicles. The epidermis is made up of several layers which are formed through mitosis. However, as these move up in strata, the outermost layers get filled with keratin and eventually the outer layer is made up of dead cells. Thus, the correct answer is option D.