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 （大腦） 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 本文敘述了當你看見某人打哈欠的時候你第一件事想要做什么？打哈欠是傳染的．但是科學家們還沒有找到原因，只知道一個人打哈欠，他附近的人也想打哈欠．
解答 52．B：語意猜測題．根據對第一段內容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，可知劃線部分的意思是從一個人傳到另一個人，故選擇B．
53．D：細節理解題．根據第二段內容The earliest yawn takes place when a baby is still inside its mother．可知還在媽媽肚子里的時候就開始打哈欠，故選擇D．
54．D：細節理解題．根據對整篇文中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 （大腦） 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，可知人們打哈欠是因為他們感覺累；使他們的大腦冷靜下來；并且排除二氧化碳，故選擇D．
55．D：細節理解題．根據對這篇文章Scientists have found that all people yawn的理解，可知我們可能在科學雜志是上讀到．故選擇D．
點評 在做英語閱讀時，首先通讀全文，不要被某個或某些自己不熟悉的單詞所困擾，了解大概意思．然后看問題，帶著問題精讀全文，同時選擇答案，必要時用排除法
