Final answer:
Keratins are fibrous proteins found in various tissues, but not in bones, which contain the protein collagen instead.
Step-by-step explanation:
Keratins are a group of tough, fibrous proteins critical to the structure of several types of body tissues. When considering options A to E, keratin is not found in bones. This is because bones mainly contain the protein collagen, which gives them their structure and strength. On the other hand, keratins play a significant role in the structure of the cornea, which is the transparent front part of the eye, as well as in components such as hair, feathers, and the lining of epithelial tissues such as the skin, mouth, and nose.