Fact 1: Most invertebrates have a more complex nervous system.

Fact 2: Invertebrates are animals without a backbone.

Given the two facts above, answer the question "what mostly have a more complex nervous system?" with the following options: 
- nerve cells
 - protist
 - animals without backbone
 - remains of prehistoric life
 - members of their own species
 - sensory neurons
 - Veins and arteries.
 - bacteria


 

   animals without backbone      