You are presented with the quiz "What by predators cause porcupines to extend their quills?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "threatening behavior by predators causes a porcupine to extend its quills" and "aggression is active, harmful and offensive, threatens all and benefits none". 

So, what's the best answer to the question?


 

    aggression       