Fact 1: Fish have a centralized nervous system with a brain.

Fact 2: Vertebrates have the most defined and developed nervous system.

Given the two facts above, answer the question "What are vertebrates?" with the following options: 
- voles
 - pigs
 - otters
 - fish
 - toads
 - koalas
 - Birds
 - humans


 

    fish     