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 "Animals that tend to have complex nervous systems are missing what?" with the following options: 
- Energy
 - Energy.
 - nervous system
 - Chlorophyll
 - backbone
 - alleles
 - abdomen
 - brain


 

     backbone    