You are presented with the question "What by predators cause porcupines to extend their quills?" and the following answer choices: 
- hypothyroidism
 - killing insects
 - kisses
 - aggression
 - love
 - hyperthyroidism
 - kinetic energy
 - cohabitating

Now knowing that threatening behavior by predators causes a porcupine to extend its quills and aggression is active, harmful and offensive, threatens all and benefits none, choose the best answer.


 

    aggression     