托福阅读修辞目的题是阅读考试中比较常见的一种题型，tpo则是托福阅读备考最权威的材料，所以托福小编综合二者，为大家集中整理了tpo阅读中考察的修辞目的题及其对应的解析，供大家参考使用。本文带来的是TPO18-2的修辞目的题，一起来看看吧。
TPO18-2 The mystery of yawning
Paragraph 2 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.
4. In paragraph 2 why does the author note that there were physiological changes when subjects opened their mouths or breathed deeply?
A. To present an argument in support of the tiredness theory
B. To cast doubt on the reliability of the tests that measured heart rate, muscle tension and skin conductance
C. To argue against the hypothesis that yawning provides a special way to improve alertness or raise physiological activity
D. To support the idea that opening the mouth or breathing deeply can affect blood oxygen levels
解析：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.
[2] 疲劳理论的另一个缺陷是打哈欠并不如该理论所预期的那样提高警觉性或生理活动。研究人员在(志愿者)打哈欠的前、中、后三个阶段均测量了心率、肌肉张力以及皮肤传导性，而他们测得皮肤传导性在打哈欠后的确存在一些变化，这一变化表明生理活动有轻微的增强。但是，在实验者被要求只是张开嘴或深呼吸时，皮肤传导性也发生了相似的变化。打哈欠对于生理活动的状态并无特殊作用。实验结果也对“打哈欠是由血液中氧含量下降或由血液中二氧化碳含量上升所引起的”这一论断产生了严重怀疑。志愿者被告知当他们吸入普通空气、纯氧或者是含有高于正常水平的二氧化碳的空气混合物时要想着打哈欠。如果疲劳理论是正确的，那么当人吸入额外的二氧化碳时，应该能够激发打哈欠;当吸入纯氧时应该能够抑制打哈欠。但实际上，在这两种条件下，打哈欠的频率并无任何差异，均维持在稳定的约24个每小时。另一个实验证明，即使是可以让呼吸频率翻倍的剧烈运动对于打哈欠频率也毫无影响。这再一次说明打哈欠几乎或完全与氧气无关。
以上就是托福阅读TPO18-2中的修辞目的题及其解析，大家可以在备考的时候参考复习，希望能够帮助大家的考前准备。最后前程百利祝大家都能取得理想的托福考试成绩。
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