Which оf the fоllоwing stаtements аbout kerаtin is correct? A) Keratin is a globular protein that functions primarily in oxygen transport. B) Keratin is a fibrous protein rich in α-helices and is strengthened by disulfide bonds between cysteine residues. C) Keratin is composed primarily of β-sheets and serves as the major structural protein of connective tissue. D) Keratin is a membrane protein responsible for transporting ions across epithelial cells. E) Keratin is an enzyme that catalyzes the formation of peptide bonds during protein synthesis.