Question

epidermal tissue
collagen fibers
keratinized cells
bone tissue
what are nails primarily made of?

Explanation:

Nails are part of the integumentary system. The epidermis is the outermost layer of skin. Collagen fibers are mainly in connective tissue like dermis. Bone tissue is for skeletal structure. Keratinized cells produce keratin, the main protein in nails (and hair, outer skin layer).

Answer:

Keratinized cells