打哈欠是由空气中的氧气与人体血液中的什么相结合引起的?

It seems hard to watch someone yawn（打哈欠） and not to yawn ourselves. Even reading about yawning can make you do it. Now, a new study has found why yawning has such a powerful force.
Yawning when others yawn, the study suggests, is a sign of pity and a form of social connection. Kids don’t develop this deeply rooted behavior until around age four, the study found. Kids with autism (自闭症) are less likely to catch yawns. In the most serious cases, they never do. Yawning might help doctors to see whether the children are developing rightly. The work could also lead to a better understanding of the ways that people communicate and connect.
"Emotional infection seems to be a born thing that connects us together," said Molly Helt, a graduate student in psychology at the University of Connecticut. "Yawning may be part of that." Inspiration for her study came when she tried to get her own autistic son to clear his ears on an airplane. She repeatedly yawned at him, hoping he would yawn back. He never did.
"The fact that autistic kids don’t do it might mean they’re really missing out on that emotional connection with people around them," she said. "The biggest thing people try to figure out after birth is how we become humans and understand that humans have minds that are different from others’," she added. "Autistic people never seem to understand that."
Like infectious （有感染力的）laughter and crying, scientists have found that yawning is a shared experience that promotes social connection. Helt said it could fight stress after a period of being nervous and spread a feeling of calm through a group.
小题1:What does the new study suggest, according to the first two paragraphs?

A．Yawning is a form of communication.

B．It is easy to stop yawning when you see others yawn.

C．Children follow others in yawning just after they are born.

D．Yawning has some mysterious force which is related to God.

小题2:According to Molly Helt, _________.

A．humans differ from animals because they communicate with others

B．yawning is a kind of emotional connection among humans

C．emotions are infectious, but yawning is not

D．yawning helps clear ears on planes

小题3:Which of the following is NOT true about yawning?

A．It is natural to yawn back if people around you yawn.

B．Some kids are too young to yawn after others.

C．Yawning can be used to test children’s development.

D．Kids with autism yawn easily when others yawn.

小题4:The author implies in the last paragraph that ________.

A．yawning is different from infectious laughter and crying in theory

B．it is bad manners to yawn on some social occasions

C．the more you yawn, the happier you will be

D．yawning can make people feel relaxed

If your head is overheating, you are very likely to yawn(打哈欠) soon, according to a new study that has found the main purpose of yawning is to control brain temperature. The study explains several mysteries about yawning, such as why it’s most commonly done just before and after sleeping, why certain diseases lead to too much yawning, and why breathing though the nose often stops yawning.
“Brains are like computers,” Andrew Gallup, a researcher in the department of Biology at Binghamton University who led the study, said. “They operate best when cool.”
He and his co-workers Micheal Miller and Anne Clark did researches on yawning in parakeets(长尾小鹦鹉) , which have relatively large brains, live wild in Australia, often experience temperature changes, and, most importantly, do not yawn when others yawn, as humans and some other animals do.
For the study, the scientists put parakeets under three different conditions: increasing temperature, high temperature and normal temperature. While the frequency(频率) of yawns did not increase under the latter two conditions, it increased greatly when the researchers increased the temperature.
It’s now believed yawning operates like a radiator(散热器).
If air in the atmosphere is cooler than the brain and body temperatures, taking it in quickly cools blood, which in turn cools the brain. The new findings also explain why tired people often yawn. Both tiredness and sleep loss can increase brain temperature, while yawning can cool down the brain.
In the future, researchers may focus more on brain temperature and its role in diseases and their symptoms. But the new study on yawning changes the popular idea that yawns are just signs of getting tired of something.
49. What’s the best title for the passage?
A. Why don’t people yawn at normal temperature?
B. The yawn explained—it cools your brain.
C. Yawning operates like a radiator.
D. The cause of yawning—finally found out.
50. The main reason why researchers chose parakeets to do the research is that parakeets______.
A. have very large brains
B. live wild in Australia
C. are not affected by others’ yawning
D. experience frequent temperature changes
51. The writer may suggest doing all of the following to stop yawning EXCEPT______.
A. breathing through the nose
B. turning up the heat
C. enjoying some cool wind
D. putting a cold towel on your forehead
52. In which section of a newspaper would you most probably read this passage?
A. Discovery. B. Education. C. Health. D. Mystery.