【托福阅读题型：Breathing During Sleep句子插入题】托福阅读中句子插入题是重要题型之一。根据托福阅读题型不同来进行专项练习，是短期提高托福阅读能力的有效方法。同学们需要多加练习哦!

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　　托福阅读句子插入题：Breathing During Sleep

　　【Paragraph 1】Of all the physiological differences in human sleep compared with wakefulness that have been discovered in the last decade, changes in respiratory control are most dramatic. Not only are there differences in the　level of the functioning of respiratory systems, there are even changes in how they function. Movements of the rib cage　for breathing are reduced during sleep, making the contractions of the diaphragm more important. [■] Yet because of the　physics of lying down, the stomach applies weight against the diaphragm and makes it more difficult for the diaphragm　to do its job. [■] However, there are many other changes that affect respiration when asleep.

　　【Paragraph 2】[■] During wakefulness, breathing is controlled by two interacting systems. [■]The first is an automatic,　metabolic system whose control is centered in the brain stem. It subconsciously adjusts breathing rate and depth in order to　regulate the levels of carbon dioxide (CO2) and oxygen (O2), and the acid-base ratio in the blood. The second system is the　voluntary, behavioral system. Its control center is based in the forebrain, and it regulates breathing for use in speech, singing,　sighing, and so on. It is capable of ignoring or overriding the automatic, metabolic system and produces an irregular pattern of　breathing.(Breathing During Sleep)

　　Look at the four squares [■] that indicate where the following sentence could be added to the passage.

　　To better understand breathing during sleep, it is, however, helpful to first understand how respiration works in general.

　　Where would the sentence best fit? Click on a square to add the sentence to the passage

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