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　　The Mystery of Yawning

　　哈欠谜团

　　P1: 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 at weekends, and that school children yawn more frequently in their first year at primary school than they do in kindergarten.

　　难词解析：

　　conventional adj.传统的

　　yawning n. 打哈欠

　　function n. 作用

　　boredom n. 厌倦

　　accompany v. 陪伴

　　难句解析：

　　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.]

　　根据传统理论，当人们无聊或者困倦时就会打哈欠。伴随睡眠不足或无聊的是浅呼吸，而浅呼吸会降低血液中氧的含量。

　　题目演练：

　　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.

　　A. It is the conventional theory that when people are bored or sleepy, they often experience a drop in blood oxygen levels due to their shallow breathing.

　　B. The conventional theory is that people yawn when bored or sleepy because yawning raises blood oxygen levels, which in turn raises alertness.

　　C. According to conventional theory, yawning is more likely to occur when people are bored or sleepy than when they are alert and breathing deeply.

　　D. Yawning, according to the conventional theory, is caused by boredom or lack of sleep and can be avoided through deeper breathing.

　　Answer: B

　　解题思路：

　　句子简化题

　　本句表述传统理论下，打哈欠发生的情况及其功能。这是本句主体。下面逐个找出信息

　　打哈欠发生的情况：when people are bored or sleepy

　　打哈欠的功能：increasing alertness by reversing the drop in blood oxygen levels.

　　(through deeper breathing用于指明reversing the drop in blood oxygen的方式，与主体无关;同理，用于修饰drop in blood oxygen的定语从句也是次要信息。)

　　下面用上述信息对应选项。

　　A选项错误明显，未提及句子主体yawning

　　B选项所有信息均正确对应，是正确选项。

　　C选项中的比较关系原文中并未提及。

　　D选项中的因果关系(is caused by)错误。原文仅提及人在无聊或困倦时会打哈欠，但并未提及二者之间存在因果关系。另外，D选项中指出可通过深呼吸避免打哈欠，这一表述原文中也未出现。

　　P2: 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.

　　难词解析：

　　flaw n. 缺点

　　alertness n. 警戒

　　physiological adj. 生理的

　　cast v. 计算

　　trigger v. 引发，引起

　　suppress v. 抑制

　　frequency n. 频率

　　vigorous adj. 精力充沛的

　　implication n. 含义