求一片英語短文的意思?
CAN you remember a morning when you’ve woken up to the ring of your alarm clock and wished you could stay in bed?You haven’t slept well,your eyes are bleary and your hair is a mess.Worse,you can’t stop yawning.Yawning is universal to humans and many animals.Cats,dogs and fish yawn just like humans do!Yawning is an involuntary (無意識(shí)的) action during which you open your mouth and breathe deeply.The average duration of a yawn is about 6 seconds.The purpose and cause of yawning are still a mystery.Scientists are not sure what causes a yawn.People yawn when they are tired or bored,but they also yawn when they aren’t.There are many ideas explaining why we yawn.One idea is that yawning is a way for the body to become more alert by taking in more oxygen.A yawn increases the heart rate,forces carbon dioxide out of the lungs (肺) and bloodstream,and brings oxygen to the brain.But one study showed that volunteers given a lot of oxygen did not yawn any less than before,while those given a lot of carbon dioxide did not yawn more.Another idea is that early humans used yawning as a form of communication.If one decided it was time to sleep,they would tell the others by yawning and they would do it in return to show they agreed.A third explanation comes from psychology (心理學(xué)) professor Gordon Gallup of University at Albany in New York.He said that as people yawn,they cool off their brains.“Brains are like computers,” he said.“They only operate efficiently (有效率地) and effectively when they’re cool.” Many things connected to yawning,like being tired,make the brain hot,and yawning can reduce the heat,he said.Scientists have sent people into space,but there are lots of seemingly (表面上) simple things,such as why we yawn,or hiccup,that they cannot figure out.Next time you are in class in the morning,let out a big yawn and watch to see how many of your classmates yawn in response!