Threatening behavior by predators causes a porcupine to extend its quills.
Predators kill and eat their prey.
The threat of being eaten causes a porcupine to extend its quills.
What threat would cause a porcupine to extend its quills?
[1] snow
[2] killing insects
[3] being eaten
[4] wind
[5] rain
[6] threatened
[7] sea urchins
[8] opossums