Read the following passage:

"Yawning is both one of our most familiar and mysterious behaviors. All humans and most vertebrates yawn, yet we don’t know whether this everyday activity has a physical or a social purpose.

"One possibility is that yawning is strictly a physical trigger and response. Some studies show that the frequency of yawning depends on oxygen and carbon dioxide levels and temperature. Yawning might cool the brain by pulling blood towards the mouth and neck where it is cooled by indrawn breath. It could trigger a release of hormones that elevate mood and appetite. Or the stretching that accompanies a yawn could help maintain muscle readiness to respond to danger.

"On the other hand, it’s also been suggested that yawning is primarily a way of communicating. Yawning is contagious. Research shows that seeing, hearing, and simply reading about a yawn causes observers to yawn themselves. Yawns are most catching in social creatures like humans, chimps, dogs, and parrots. They’re somewhat less catching among children with autism and adults with psychopathic tendencies, and they don’t occur at all in solitary species like tortoises. Yawning may be a way of forming bonds within a group by synching up sleep and wake cycles and other behaviors. It might also serve as a way of establishing dominance by showing off the size of teeth and jaws or signaling boredom.

"While scientists debate the purpose of yawning, one thing is almost certain. You probably yawned more than once reading about it."

Which option below is a major supporting detail in the reading?


Yawning might help cool the brain.


Yawning may be a method of communication.


Yawning is common in the animal kingdom.


Turtles don’t catch yawns.