Answer the following question given this paragraph: 

Only mammals have hair. Hair is a fiber made mainly of the tough protein keratin. The cells of each hair are filled with keratin and no longer alive. The dead cells overlap each other, almost like shingles on a roof. They work like shingles as well, by helping shed water from hair.


Q: What is the only class of animals that has hair?

 Choices:

- reptiles

- amphibians

- birds

- mammals

A:
mammals
