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根据传统理论，打哈欠发生在人们感到无聊或困倦的时候，它通过深呼吸扭转血液含氧量的下降，从而起到提高警觉性的作用，而血液含氧量的下降是由缺乏睡眠或感到无聊时的浅呼吸引起的。

According to conventional theory, yawning takes place when people are bored or sleepy and serves the function of increasing alertness by reversing, through deeper breathing, the drop in blood oxygen levels that are caused by the shallow breathing that accompanies lack of sleep or boredom.

不幸的是，对打哈欠的少数科学调查未能发现人们打哈欠的频率与他们睡了多少觉或他们有多累之间有任何联系。

Unfortunately, the few scientific investigations of yawning have failed to find any connection between how often someone yawns and how much sleep they have had or how tired they are.

几乎所有支持疲劳理论的研究都证实，成年人在工作日比周末更频繁地打哈欠，小学生在小学一年级比在幼儿园更频繁地打哈欠。

About the closest any research has come to supporting the tiredness theory is to confirm that adults yawn more often on weekdays than on weekends, and that school children yawn more frequently in their first year at primary school than they do in kindergarten.

疲劳理论的另一个缺陷是，打哈欠并不能像该理论所预测的那样提高警觉性或生理活动。

Another flaw of the tiredness theory is that yawning does not raise alertness or physiological activity, as the theory would predict.

当研究人员测量人们打哈欠前后的心率、肌肉张力和皮肤电导时，他们确实发现了打哈欠后皮肤电导的一些变化，这表明生理活动略有增加。

When researchers measured the heart rate, muscle tension and skin conductance of people before, during, and after yawning, they did detect some changes in skin conductance following yawning, indicating a slight increase in physiological activity.

然而，当受试者被要求张嘴或深呼吸时，也会发生类似的变化。

However, similar changes occurred when the subjects were asked simply to open their mouths or to breathe deeply.

打呵欠对他们的生理活动状态没有什么特殊的影响。

Yawning did nothing special to their state of physiological activity.

实验也对“打哈欠是由血液中的氧气减少或血液中的二氧化碳增加引起的”这一观点提出了严重的质疑。

Experiments have also cast serious doubt on the belief that yawning is triggered by a drop in blood oxygen or a rise in blood carbon dioxide.

志愿者们被告知在呼吸正常空气、纯氧或二氧化碳浓度高于正常水平的混合空气时想着打哈欠。

Volunteers were told to think about yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.

如果这个理论是正确的，那么呼吸含有额外二氧化碳的空气应该会引起打哈欠，而呼吸纯氧应该会抑制打哈欠。

If the theory was correct, breathing air with extra carbon dioxide should have triggered yawning, while breathing pure oxygen should have suppressed yawning.

事实上，这两种情况对打哈欠的频率都没有影响，打哈欠频率保持在每小时24次左右。

In fact, neither condition made any difference to the frequency of yawning, which remained constant at about 24 yawns per hour.

另一项实验表明，剧烈运动可以使呼吸频率增加一倍，但对打哈欠的频率没有影响。

Another experiment demonstrated that physical exercise, which was sufficiently vigorous to double the rate of breathing, had no effect on the frequency of yawning.

再一次，这意味着打哈欠与氧气几乎没有关系。

Again, the implication is that yawning has little or nothing to do with oxygen.

另一种完全不同的理论认为，打呵欠有助于生命早期肺部的生理发育，但对成年人没有任何剩余的生理功能。

A completely different theory holds that yawning assists in the physical development of the lungs early in life, but has no remaining biological function in adults.

有人认为打哈欠和打嗝可能有助于清理胎儿的气道。

It has been suggested that yawning and hiccupping might serve to clear out the fetus’s airways.

胎儿的肺会分泌一种与母亲的羊水混合的液体。

The lungs of a fetus secrete a liquid that mixes with its mother’s amniotic fluid.

有先天性阻塞阻止这种液体从肺部流出的婴儿有时会有畸形的肺部。

Babies with congenital blockages that prevent this fluid from escaping from their lungs are sometimes born with deformed lungs.

打哈欠可能通过周期性地降低肺部的压力来帮助清理肺部。

It might be that yawning helps to clear out the lungs by periodically lowering the pressure in them.

根据这一理论，成年人打呵欠只是发育的“化石”，没有生物学功能。

According to this theory, yawning in adults is just a developmental fossil with no biological function.

但是，尽管我们承认并不是生活中的每件事都可以用达尔文进化论来解释，我们还是有充分的理由对像这样的理论持怀疑态度，因为这些理论回避了打哈欠对成年人有什么影响的问题。

But, while accepting that not everything in life can be explained by Darwinian evolution, there are sound reasons for being skeptical of theories like this one, which avoid the issue of what yawning does for adults.

打呵欠会分散注意力，消耗精力，耗费时间。

Yawning is distracting, consumes energy and takes time.

几乎可以肯定，它在成人和胎儿身上都起着重要的作用。

It is almost certainly doing something significant in adults as well as in fetuses.

经验证据表明，打哈欠有一个完全不同的功能，即打哈欠使我们为活动水平的变化做好准备。

The empirical evidence, such as it is, suggests an altogether different function for yawning—namely, that yawning prepares us for a change in activity level.

这一理论的支持来自于对日常生活中打哈欠行为的研究。

Support for this theory came from a study of yawning behavior in everyday life.

志愿者们在长达两周的时间里，佩戴腕带设备，自动记录他们的身体活动；志愿者们还通过在每次打哈欠时按下设备上的一个按钮来记录他们的打哈欠。

Volunteers wore wrist-mounted devices that automatically recorded their physical activity for up to two weeks; the volunteers also recorded their yawns by pressing a button on the device each time they yawned.

数据显示，打哈欠往往发生在一段行为活动增加之前15分钟左右。

The data showed that yawning tended to occur about 15 minutes before a period of increased behavioral activity.

然而，打哈欠与睡眠模式没有关系。

Yawning bore no relationship to sleep patterns, however.

这与坊间流传的证据相符，即人们在既不累也不无聊，只是为即将到来的精神和身体活动做准备的情况下经常打哈欠。

This accords with anecdotal evidence that people often yawn in situations where they are neither tired nor bored, but are preparing for impending mental and physical activity.

这种打哈欠通常被认为是“不协调的”，因为它似乎不合适，至少在疲劳的观点上是这样的：士兵在战斗前打哈欠，音乐家在表演前打哈欠，运动员在比赛前打哈欠。

Such yawning is often referred to as “incongruous” because it seems out of place, at least on the tiredness view: soldiers yawning before combat, musicians yawning before performing, and athletes yawning before competing.

他们打呵欠似乎与困倦或厌烦没有任何关系——恰恰相反——但它确实预示着活动水平的变化。

Their yawning seems to have nothing to do with sleepiness or boredom—quite the reverse—but it does precede a change in activity level.

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

In paragraph 1, what point does the author make about the evidence for the tiredness theory of yawning?

The word “flaw” in the passage is closest in meaning to

In paragraph 2, why does the author note that there were physiological changes when subjects opened their mouths or breathed deeply?

The word “triggered” in the passage is closest in meaning to

Paragraph 2 answers all of the following questions about yawning EXCEPT:

The word “periodically” in the passage is closest in meaning to

According to the developmental theory of yawning presented in paragraph 3, what is the role of yawning?

Paragraph 3 supports which of the following statements about the developmental theory of yawning?

The word “empirical” in the passage is closest in meaning to

The study of yawning behavior discussed in paragraph 4 supports which of the following conclusions?

Why does the author mention “soldiers yawning before combat, musicians yawning before performing, and athletes yawning before competing”?

Look at the four squares  that indicate where the following sentence could be added to the passage. This, however, was not the case.  Where would the sentence best fit? Click on a square  to add the sentence to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

The Mystery of Yawning According to conventional theory, yawning takes place when people are bored or sleepy and serves the function of increasing alertness by reversing, through deeper breathing, the drop in blood oxygen levels that are caused by the shallow breathing that accompanies lack of sleep or boredom. Unfortunately, the few scientific investigations of yawning have failed to find any connection between how often someone yawns and how much sleep they have had or how tired they are. About the closest any research has come to supporting the tiredness theory is to confirm that adults yawn more often on weekdays than on weekends, and that school children yawn more frequently in their first year at primary school than they do in kindergarten. Another flaw of the tiredness theory is that yawning does not raise alertness or physiological activity, as the theory would predict. When researchers measured the heart rate, muscle tension and skin conductance of people before, during, and after yawning, they did detect some changes in skin conductance following yawning, indicating a slight increase in physiological activity. However, similar changes occurred when the subjects were asked simply to open their mouths or to breathe deeply. Yawning did nothing special to their state of physiological activity. Experiments have also cast serious doubt on the belief that yawning is triggered by a drop in blood oxygen or a rise in blood carbon dioxide.  Volunteers were told to think about yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.  If the theory was correct, breathing air with extra carbon dioxide should have triggered yawning, while breathing pure oxygen should have suppressed yawning.  In fact, neither condition made any difference to the frequency of yawning, which remained constant at about 24 yawns per hour.  Another experiment demonstrated that physical exercise, which was sufficiently vigorous to double the rate of breathing, had no effect on the frequency of yawning. Again, the implication is that yawning has little or nothing to do with oxygen. A completely different theory holds that yawning assists in the physical development of the lungs early in life, but has no remaining biological function in adults. It has been suggested that yawning and hiccupping might serve to clear out the fetus’s airways. The lungs of a fetus secrete a liquid that mixes with its mother’s amniotic fluid. Babies with congenital blockages that prevent this fluid from escaping from their lungs are sometimes born with deformed lungs. It might be that yawning helps to clear out the lungs by periodically lowering the pressure in them. According to this theory, yawning in adults is just a developmental fossil with no biological function. But, while accepting that not everything in life can be explained by Darwinian evolution, there are sound reasons for being skeptical of theories like this one, which avoid the issue of what yawning does for adults. Yawning is distracting, consumes energy and takes time. It is almost certainly doing something significant in adults as well as in fetuses. What could it be? The empirical evidence, such as it is, suggests an altogether different function for yawning—namely, that yawning prepares us for a change in activity level. Support for this theory came from a study of yawning behavior in everyday life. Volunteers wore wrist-mounted devices that automatically recorded their physical activity for up to two weeks; the volunteers also recorded their yawns by pressing a button on the device each time they yawned. The data showed that yawning tended to occur about 15 minutes before a period of increased behavioral activity. Yawning bore no relationship to sleep patterns, however. This accords with anecdotal evidence that people often yawn in situations where they are neither tired nor bored, but are preparing for impending mental and physical activity. Such yawning is often referred to as “incongruous” because it seems out of place, at least on the tiredness view: soldiers yawning before combat, musicians yawning before performing, and athletes yawning before competing. Their yawning seems to have nothing to do with sleepiness or boredom—quite the reverse—but it does precede a change in activity level.