According toconventionaltheory, yawning takes place when people are bored or sleepy and serves thefunctionof increasing alertness by reversing,throughdeeperbreathing, thedropin bloodoxygenlevels that are caused by theshallowbreathingthat accompanieslackof sleep or boredom. Unfortunately, the fewscientificinvestigations 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 tirednesstheoryis toconfirmthat adults yawn more often on weekdays than at weekends, and that school children yawn more frequently in their first year atprimaryschool than they do in kindergarten.

Anotherflawof the tirednesstheoryis that yawning does notraisealertness orphysiologicalactivity, as thetheorywouldpredict. When researchers measured the heartrate,muscletensionand skinconductanceof people before, during and after yawning, they diddetectsome changes in skinconductancefollowing yawning, indicating aslightincrease inphysiologicalactivity. However,similarchanges occurred when the subjects were askedsimplyto open their mouths or to breathe deeply. Yawning did nothingspecialto theirstateofphysiologicalactivity. Experiments have alsocastseriousdoubton the belief that yawning is triggered by adropin bloodoxygenor a rise in bloodcarbondioxide. Volunteers were told to think about yawning while they breathed either normalair,pureoxygen, or anairmixture with an above-normallevelofcarbondioxide. If thetheorywas correct,breathingairwithextracarbondioxideshould have triggered yawning, whilebreathingpureoxygenshould have suppressed yawning. In fact, neither condition made anydifferenceto thefrequencyof yawning, which remainedconstantat about 24 yawns per hour. Another experiment demonstrated thatphysicalexercise, which wassufficientlyvigorousto double therateofbreathing, had no effect on thefrequencyof yawning. Again theimplicationis that yawning has little or nothing to do withoxygen.

A completely differenttheoryholds that yawning assists in thephysicaldevelopmentof the lungs early in life, but has noremainingbiologicalfunctionin adults. It has been suggested that yawning and hiccupping might serve toclearout the fetuses airways. The lungs of afetussecretealiquidthat mixes with its mother's amnioticfluid. Babies withcongenitalblockages that prevent thisfluidfrom escaping from their lungs are sometimes born with deformed lungs. It might be that yawning helps toclearout the lungs byperiodicallylowering thepressurein them. According to thistheory, yawning in adults is just a developmentalfossilwith no biologicalfunction. But, while accepting that not everything in life can be explained by Darwinianevolution, there aresoundreasons for beingskepticalof theories like this one, whichavoidtheissueof what yawning does for adults. Yawning is distracting, consumes energy and takes time. It is almost certainly doing somethingsignificantin adults as well as in fetuses. What could it be?

Theempiricalevidence, such as it is, suggests analtogetherdifferentfunctionfor yawning—namely, that yawning prepares us for a change inactivitylevel. Support for thistheorycame from a study of yawningbehaviorin everyday life. Volunteers wore wrist-mounted devices that automatically recorded theirphysicalactivityfor up to two weeks: the volunteers also recorded their yawns by pressing a button on thedeviceeach time they yawned. Thedatashowed that yawning tended tooccurabout 15 minutes before a period of increasedbehavioralactivity. Yawning bore no relationship to sleep patterns, however. This accords withanecdotalevidencethat people often yawn in situations where they are neither tired nor bored, but are preparing forimpendingmentalandphysicalactivity. Such yawning is often referred to as "incongruous" because it seems out of place, atleaston the tiredness view: soldiers yawning beforecombat, musicians yawning before performing, and athletes yawning beforecompeting. Their yawning seems to have nothing to do with sleepiness or boredom—quite thereverse—but it doesprecedea change inactivitylevel.

Questions:
question_stem: 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.
choices: tag: A
text: 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.

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

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

tag: D
text: Yawning, according to the conventional theory, is caused by boredom or lack of sleep and can be avoided through deeper breathing.
answer_key: B
explanation: B 原文的主要逻辑是并列，表达出两层意思：1）yawn 是因为 bored or sleepy；2）能够起到提神的作用。所以 B 正确。A 缺失了第二层意思；C 的比较是原文没有的；D 的 can be avoided 原文没说。

question_stem: In paragragh1, what point does the author make about the evidence for the tiredness theory of yawning?
choices: tag: A
text: There is no scientific evidence linking yawning with tiredness.

tag: B
text: The evidence is wide-ranging because it covers multiple age-groups.

tag: C
text: The evidence is reliable because it was collected over a long period of time.

tag: D
text: The evidence is questionable because the yawning patterns of children and adults should be different.
answer_key: A
explanation: A 接上题，第一句说传统理论认为打呵欠与累和无聊有关，这正是本题问的 tiredness theory，所以往下看，下一句说没有证据证明这个理论，所以答案是 A，原文明确说没有证据，BCD 都说有 evidence，错。

question_stem: The word “flaw” in the passage is closest in meaning to
choices: tag: A
text: fault

tag: B
text: aspect

tag: C
text: confusion

tag: D
text: mystery
answer_key: A
explanation: A, flaw: 瑕疵，缺点，错误。A 是错误；B 是方面；C 是困惑；D 是秘密。所以 A 的 fault 正确。

question_stem: In the paragraph 2, why does the author note that there were physiological changes when subjects opened their mouths or breathed deeply?
choices: tag: A
text: To present an argument in support of the tiredness theory

tag: B
text: To cast doubt on the reliability of the tests that measured heart rate, muscle tension and skin conductance

tag: C
text: To argue against the hypothesis that yawning provides a special way to improve alertness or raise physiological activity

tag: D
text: To support the idea that opening the mouth or breathing deeply can affect blood oxygen levels
answer_key: C
explanation: C 修辞目的题，首先找到修辞点所在的第三句，本句只是在重复这个例子，没有观点性的东西，往前看。前句说测到了一些生理上的变化，还是在说例子，所以看中心句，也就是第一句，说打呵欠根本不会提高清醒程度，所以答案是 C。A 和 D 反了，B 说质疑实验的可靠性，作者不是质疑实验本身，而是质疑结论，并用实验支持这个质疑。

question_stem: The word “triggered” in the passage is closest in meaning to
choices: tag: A
text: removed

tag: B
text: followed

tag: C
text: increased

tag: D
text: caused
answer_key: D
explanation: D trigger: 引起，激发。A 是移除；B 是跟着；C 是增加；D 是引起。所以 D 的 cause 正确。

question_stem: Paragraph 2 answers all of the following questions about yawning EXCEPT
choices: tag: A
text: Does yawning increase alertness or physiological activity?

tag: B
text: Does thinking about yawning increase yawning over not thinking about yawning?

tag: C
text: Does the amount of carbon dioxide and oxygen in the air affect the rate at which people yawn?

tag: D
text: Does the rate of breathing affect the rate at which people yawn?
answer_key: B
explanation: B  EXCEPT 题，排除法，A 的 alertness or physiological activity 做关键词定位至第一句，正确，不选；B 的 thinking about yawning 做关键词定位至倒数第三句，没有说是否 increase，所以 B 没说，选；C 的 rate of yawning 做关键词定位至倒数第二句，正确，不选；D 的 rate of breathing 做关键词定位至最后一句，D 正确，不选。

question_stem: The word “periodically” in the passage is closest in the meaning to
choices: tag: A
text: continuously

tag: B
text: quickly

tag: C
text: regularly

tag: D
text: carefully
answer_key: C
explanation: C periodically: 规律地，周期性的。A 是持续地；B 是快速地；C 是定期地，有规律的；D 是认真地。所以 C 的 regularly 正确。

question_stem: According to the developmental theory of yawning presented in paragraph 3, what is the role of yawning?
choices: tag: A
text: It caused hiccups, which aid in the development of the lungs.

tag: B
text: It controls the amount of pressure the lungs place on other developing organs.

tag: C
text: It prevents amniotic fluid from entering the lungs.

tag: D
text: It removes a potentially harmful fluid from the lungs.
answer_key: D
explanation: D 以 developmental theory 做关键词定位至第一句，说打呵欠在生命的早期是有用的，但对成人没用，但这句只是单纯在说理论，往下看。下一句说打嗝和打呵欠能帮助胎儿清理呼吸道，所以答案是 D。A 明显没说；B 的 other developing organ 没说；C 的 prevent 没说。

question_stem: Paragraph 3 supports which of the following statements about the development theory of yawning?
choices: tag: A
text: The theory is attractive because it explains yawning from the perspective of Darwinian evolution.

tag: B
text: The theory is unsatisfactory because it cannot explain the lung deformities of infants.

tag: C
text: The theory is questionable because it does not explain why a useless and inconvenient behavior would continue into adulthood.

tag: D
text: The theory is incomplete because it does not explain all the evolutionary stages in the development of yawning.
answer_key: C
explanation: C 此题排除法较容易解，理由是问到整段可以看首句，但首句我们刚才已经看过了，没用。B 的 lung deformity 做关键词定位至第四句，但完全没说是否解释；D 的 evolutionary stage 原文完全没说，不选。

question_stem: The word “empirical” in the passage is closest in meaning to
choices: tag: A
text: reliable

tag: B
text: based on common sense

tag: C
text: relevant

tag: D
text: based on observation
answer_key: D
explanation: D empirical: 实证的。A 是可靠的；B 是根据常识；C 是相关的；D 是基于观察（所得）。所以答案是 D 的 based on observation。

question_stem: The study of yawning behavior discussed in paragraph 4 supports which of the following conclusions?
choices: tag: A
text: Yawning is associated with an expectation of increased physical activity.

tag: B
text: Yawning occurs more frequently when people are asked to record their yawning.

tag: C
text: People tend to yawn about fifteen minutes before they become tired or bored.

tag: D
text: Mental or physical stress tends to make people yawn.
answer_key: A
explanation: A 问整段的结论，看开头句，说事实证明，打呵欠的作用是表面活动水平的变化，所以答案是 A，increased activity；BCD 都完全没说，而且也不是整段的结论。

question_stem: Why does the author mention “soldiers yawning before combat, musicians yawning before performing, and athletes yawning before competing”?
choices: tag: A
text: To argue that just the expectation of physical activity can make some people feel tired

tag: B
text: To explain how the view that people yawn because they are tired accounts for yawning before stressful situations

tag: C
text: To support the view that yawning helps prepare a person for mental or physical exertion

tag: D
text: To provide anecdotal evidence that conflicts with the experience of the volunteers in the study
answer_key: C
explanation: C，修辞目的题，先看修辞点所在句子，发现只是单纯陈述一个例子，继续往前看，上句说人们打呵欠既不是因为困也不是因为累，而是为了精神上活身体上的活动做准备，所以答案是 C。A 的 expectation，B 的 stressful situation 和 D 的 conflict 原文都没说。