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 have more complex nervous systems" with the following options: 
- animals without a backbone
 - the wearing away of rock
 - h2o
 - barks and snarls
 - plants
 - density
 - Veins and arteries.
 - remains of prehistoric life


 

 animals without a backbone        