Keratin is found in which of the following locations?

Keratin is a fibrous structural protein that plays a crucial role in the composition of various biological materials. It is most commonly associated with tough and protective structures in animals. Each of the provided locations—hair, hooves, and feathers—contains keratin, which serves specific functions in those areas.

Hair is primarily composed of keratin, providing strength and protection for the skin. Hooves, found in various livestock, are also made of keratin, which helps protect the sensitive structures within and provides support during movement. Feathers, which are unique to birds, are constructed of keratin as well, offering insulation and aiding in flight.

Since keratin is a common component in all these structures, the correct response encompasses all the answer choices. This illustrates the widespread presence of keratin in animal biology, highlighting its importance in maintaining the integrity and functionality of skin appendages.