Answer:
Option B, skin
Step-by-step explanation:
The root phrases "kerat-" and "kerat/o-" refer to the protein keratin which is essential to the structure of the nails, hair, and skin, protecting them from abrasion. Without keratin, the skin is not as strong nor is it as elastic, and proliferation of epithelial cells is less controlled.
The common root phrases representing bone are oste/o- and ossicul/o-. Cardi/o- denotes the heart. Hem/o- is a common root phrase for blood.