4．What is the first thing you want to do when you see someone yawn（打哈欠）？You want to yawn，too!Yawning is contagious．
Scientists have found that all people yawn．Babies start to yawn even before they are horn．The earliest yawn takes place when a baby is still inside its mother．When young children are about one year old，they start to yawn when they see others yawning．That's why scientists seem to think yawning is contagious．
It's no secret that yawning is contagious，but why do we yawn？Well，scientists are not really sure．
Some think we yawn because we feel bored．Recently scientists studied two groups of students between the ages of 17and 19．One group watched music videos，and the other watched a boring color test．Scientists compared the numbers of their yawns and found that the color test group yawned more times than the video group．
Another reason about yawning has to do with breathing．Some scientists believe that when we are bored or tired，we breathe more slowly．As our breathing slows down，we cannot get rid of（去除） enough carbon dioxide （CO2） in our bodies．When there is too much carbon dioxide，our bodies will tell the brains （大脑） to breathe deeply．The result is a big yawn．
In 2007，scientists suggested a new reason．They said that the reason people yawned was to cool down their brains．These scientists found that people who were warmer than others yawned more often．
Scientists are still trying to find out why yawning happens and why it is so contagious．But they are only sure that when one person yawns，almost everyone else nearby wants to yawn，too．
52．The underlined word"contagious"in Paragraph 1 meansB．
A．helpful to our health B．passing from one person to another
C．hard to understand D．getting into one trouble after another
53．According to the scientists，people start to yawn when they areD．
A．born B．one year old
C.17or 19years old D．inside their mothers
54．Which of the following are the possible reasons about yawning according to the passage？D
①People yawn because they are bored．②People yawn to catch others'attention．
③People yawn to cool down their brains．④People yawn to get rid of carbon dioxide．
a．①②③B．②③④C．①②④D．①③④
55．We can probably read this passage in aD．
A．story book B．travel guidebook
C．movie poster D．science magazine．
分析 本文叙述了当你看见某人打哈欠的时候你第一件事想要做什么？打哈欠是传染的．但是科学家们还没有找到原因，只知道一个人打哈欠，他附近的人也想打哈欠．
解答 52．B：语意猜测题．根据对第一段内容What is the first thing you want to do when you see someone yawn（打哈欠）？You want to yawn，too!的理解，可知划线部分的意思是从一个人传到另一个人，故选择B．
53．D：细节理解题．根据第二段内容The earliest yawn takes place when a baby is still inside its mother．可知还在妈妈肚子里的时候就开始打哈欠，故选择D．
54．D：细节理解题．根据对整篇文中Some scientists believe that when we are bored or tired，we breathe more slowly．As our breathing slows down，we cannot get rid of（去除） enough carbon dioxide （CO2） in our bodies．When there is too much carbon dioxide，our bodies will tell the brains （大脑） to breathe deeply．The result is a big yawn．In 2007，scientists suggested a new reason．They said that the reason people yawned was to cool down their brains的理解，可知人们打哈欠是因为他们感觉累；使他们的大脑冷静下来；并且排除二氧化碳，故选择D．
55．D：细节理解题．根据对这篇文章Scientists have found that all people yawn的理解，可知我们可能在科学杂志是上读到．故选择D．
点评 在做英语阅读时，首先通读全文，不要被某个或某些自己不熟悉的单词所困扰，了解大概意思．然后看问题，带着问题精读全文，同时选择答案，必要时用排除法
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