You are presented with the question "Animals that tend to have complex nervous systems are missing what?" and the following answer choices: 
- Energy
 - Energy.
 - nervous system
 - Chlorophyll
 - backbone
 - alleles
 - abdomen
 - brain

Now knowing that most invertebrates have a more complex nervous system and invertebrates are animals without a backbone, choose the best answer.


 

     backbone    