Answer the following question given this paragraph: 

Vertebrates. From the smallest of fish to us. One of the main features we all have in common is our backbone. Vertebrates describes main biological features of fish, amphibians, reptiles, birds, and mammals.


Q: Vertebrates. from the smallest of fish to us. one of the main features we all have in common is our what?

 Choices:

- hair

- warm blood

- laying eggs

- backbone

A:
backbone
