Answer:
The correct answer is option A, that is, keratin.
Step-by-step explanation:
Keratin refers to a protein that belongs to one of the families of fibrous structural proteins. It is the essential structural substance that forms nails, hair, horns, feathers, external layer of the skin, and hooves. It is the protein, which safeguards epithelial cells from stress or destruction. Keratin is tremendously insoluble in organic solvents and water.