Given a scientific question, generate a correct answer to it.

Ex Input:
What term is used to describe muscle fibers that allows muscles to contract?

Ex Output:
organelle

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

Ex Output:
backbone

Ex Input:
What is an organic compound made up of small molecules called amino acids called?

Ex Output:
a protein