question: What is a fiber that is found only in mammals?
distractor3: feathers
distractor1: muscle
distractor2: muscle
correct_answer: hair
support: Hair is a fiber that is found only in mammals. Its main component is keratin. A hair shaft consists of dead, keratin-filled cells that overlap each other like the shingles on a roof (see Figure below ). Like roof shingles, the overlapping cells help shed water from the hair.