Of all thephysiologicaldifferences in human sleep compared with wakefulness that have been discovered in the lastdecade, changes inrespiratorycontrol are mostdramatic. Not only are there differences in thelevelof the functioning ofrespiratorysystems, there areevenchanges in how theyfunction. Movements of the rib cage forbreathingare 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 thataffectrespirationwhen asleep.

During wakefulness,breathingis controlled by two interacting systems. The first is anautomatic,metabolicsystem whose control is centered in the brainstem. It subconsciously adjustsbreathingrateand depth in order toregulatethe levels ofcarbondioxide(CO2) andoxygen(O2), and the acid-baseratioin the blood. Thesecondsystem is the voluntary,behavioralsystem. Its control center is based in the forebrain, and it regulatesbreathingfor use in speech, singing, sighing, and so on. It iscapableof ignoring oroverridingtheautomatic,metabolicsystem and produces anirregularpatternofbreathing.

During NREM (thephaseof sleep in which there is no rapid eye movement)breathingbecomes deeper and moreregular, but there is also adecreasein thebreathingrate, resulting in lessairbeing exchangedoverall. This occurs because during NREM sleep theautomatic,metabolicsystem hasexclusivecontrol overbreathingand the body uses lessoxygenand produces lesscarbondioxide. Also, during sleep theautomaticmetabolicsystem is less responsive tocarbondioxidelevels andoxygenlevels in the blood. Two things result from these changes inbreathingcontrol thatoccurduring sleep. First, there may be abriefcessation orreductionofbreathingwhen falling asleep as the sleeper waxes and wanes between sleep and wakefulness and their differing control mechanisms. Second, once sleep is fully obtained, there is an increase ofcarbondioxideand adecreaseofoxygenin the blood that persists during NREM.

But that is not all that changes. During all phases of sleep, several changes in theairpassages have been observed. It takes twice as much effort to breathe during sleep because of greaterresistancetoairflowin the airways and changes in theefficiencyof the muscles used forbreathing. Some of the muscles that help keep the upper airway open whenbreathingtendto become more relaxed during sleep, especially during REM (thephaseof sleep in which there is rapid eye movement). Without thismuscularaction, inhaling is like suckingairout of a balloon—the narrow passagestendtocollapse. Also there is aregularcycleof change inresistancebetween the two sides of the nose. If something blocks the "good" side, such ascongestionfrom allergies or a cold, thenresistanceincreasesdramatically. Coupled with these factors is the loss of thecomplexinteractions among the muscles that can change therouteofairflowfrom nose to mouth.

Otherrespiratoryregulating mechanisms apparentlyceasefunctioning during sleep. For example, during wakefulness there is animmediate,automatic,adaptiveincrease inbreathingeffort when inhaling is made more difficult (such asbreathingthrougha restrictive facemask). This reflexiveadjustmentis totally absent during NREM sleep. Only after several inadequate breaths under such conditions, resulting in theconsiderableelevationofcarbondioxideandreductionofoxygenin the blood, isbreathingeffort adjusted. Finally, the coughing reflex inreactionto irritants in the airway produces not a cough during sleep but a cessation ofbreathing. If theirritationissevereenough, a sleeping person willarouse,clearthe airway, thenresumebreathingand likely return to sleep.

Additionalbreathingchangesoccurduring REM sleep that areevenmoredramaticthan the changes thatoccurduring NREM. Theamountofairexchanged isevenlowerin REM than NREM because, althoughbreathingis more rapid in REM, it is also moreirregular, withbriefepisodes ofshallowbreathingorabsenceofbreathing. Inaddition,breathingduring REM depends much more on theactionof the diaphragm and much less on rib cageaction.

Questions:
question_stem: According to paragraph 1, which of the following can be inferred about the diaphragm during sleep?
choices: tag: A
text: During sleep the diaphragm requires increased movement of the rib cage.

tag: B
text: The diaphragm helps with breathing as movements of the rib cage decrease during sleep.

tag: C
text: The diaphragm requires a great amount of pressure to function properly.

tag: D
text: The diaphragm contributes to the effective functioning of the rib cage.
answer_key: B
explanation: B 以 diaphragm 做关键词定位至第三句和第四句，说 ribcage 运动变少，使得 diaphragm 更重要，但 stomach 的压力使得 diaphragm 工作起来更困难，B 是正确答案。A 的 increased movement of the rib cage 和 C 的需要 pressure 都与原文相反；D 说 diaphragm contributes to 原文没有说

question_stem: According to paragraph 2, all of the following are true of the voluntary breathing system EXCEPT:
choices: tag: A
text: It has its control center in the brain stem.

tag: B
text: It controls breathing for a number of activities during wakefulness.

tag: C
text: It is able to bypass the automatic system.

tag: D
text: It produces an irregular breathing pattern.
answer_key: A
explanation: A  EXCEPT 题，排除法。A 的 centered in brainstem 做关键词定位至第一句，但原文说这个特点是属于 automatic，metabolic system 的，而 voluntary 的 center 是在 forebrain，所以 A 错，选；B 的 a number of activities 做关键词定位至倒数第二句的一大堆活动，所以 B 正确，不选；C 的 bypass the automatic system 和 D 的 irregular breathing pattern 做关键词都定位至最后一句，都正确，不选

question_stem: The word "exclusive" in the passage (paragraph 3) is closest in meaning to
choices: tag: A
text: consistent

tag: B
text: perfect

tag: C
text: partial

tag: D
text: sole
answer_key: D
explanation: D exclusive: 独有的，排外的。A 是始终如一的，一致的，B 是完美的，C 是部分的，D 是唯一的，独有的。所以正确答案是 sole。

question_stem: According to paragraph 3, which of the following may occur just before NREM sleep begins?
choices: tag: A
text: The automatic, metabolic system may increase its dependence on air exchanges.

tag: B
text: Breathing can stop for a short time as a person falls asleep.

tag: C
text: An increase in the oxygen level in the blood can occur as sleep becomes fully obtained.

tag: D
text: The level of carbon dioxide in the blood may drop suddenly.
answer_key: B
explanation: B 此题关键词难找，可以顺序向下看，也可以用排除法，如果顺序向下看的话，会看到第一点说的是当 sleeper 在睡与醒之间摇摆的时候，发生了呼吸 cessation，也就是 stop，所以正确答案是 B，stop for a short time。C 和 D 一个说氧上升一个说二氧化碳下降，是一回事，都不是在睡觉期间发生的，所以都反了，而且两个一样的也都不选，A 没说。

question_stem: What is the author's purpose in stating that inhaling is like sucking air out of a balloon?
choices: tag: A
text: To refute the argument that additional effort is necessary for breathing during sleep

tag: B
text: To argue that REM sleep is more important than NREM sleep

tag: C
text: To illustrate the difficulty of breathing during sleep

tag: D
text: To illustrate how blockage of narrow passages can be prevented during sleep
answer_key: C
explanation: 作者为什么说到呼吸就像从气球中吸气一样。先看修辞点所在的句子，说如果没有这种肌肉活动，呼吸就像从气球中吸气一样；作者用了类比的修辞（like），所以我们需要知道作者把什么和该句做类比，继续往前看；前一句说：在睡觉时，肌肉会变得放松；好像看不出什么联系，再往前看一句，说在睡觉期间呼吸要花费更多的努力，其中一个原因是肌肉效率的变化，所以作者想强调的就是呼吸期间呼吸很困难，故正确答案是 C。A 的 refute 与原文相反；B 的比较和 D 的 prevent blockage 都是无中生有。

question_stem: All of the following are mentioned in paragraph 4 as being characteristic of breathing during sleep EXCEPT
choices: tag: A
text: relaxation of the muscles involved in the respiratory system

tag: B
text: changes in resistance between the two sides of the nose

tag: C
text: easier airflow in the passages of the upper airway

tag: D
text: absence of certain complex muscle interactions
answer_key: C
explanation: C  EXCEPT 题，排除法。A 的 relaxation of the muscles 做关键词定位至第三句，正确，不选；B 的 two sides of the nose 做关键词定位至倒数第三句，正确，不选；C 的 upper airway 做关键词定位至第三句，但答案的 easier airflow 原文完全没说，C 错，选；D 的 complex muscle interaction 做关键词都定位至最后一句，正确，不选

question_stem: According to paragraph 5, what happens during NREM sleep when inhaling is difficult?
choices: tag: A
text: There is an immediate, automatic, adaptive increase in breathing effort.

tag: B
text: The sleeping person takes several inadequate breaths before the breathing effort is adjusted.

tag: C
text: The coughing reflex causes the breathing effort to adjust.

tag: D
text: The airways become cleared as the blood removes irritants.
answer_key: B
explanation: B 以 inhaling is difficult 做关键词定位至第二句，但这句只说了 difficult 的事儿，没说发生了什么，往下看。下句说 NREM 期间什么 adjustment 都没有，只有在 inadequate breaths 之后才 adjust，所以答案是 B。A 是 wakeful 时候才有的；C 的因果关系原文没说；D 完全没说.

question_stem: It can be inferred from paragraph 5 that a very mild irritation during sleep will likely cause the sleeping person to
choices: tag: A
text: increase the breathing effort

tag: B
text: wake up and remove the source of irritation

tag: C
text: cough while still sleeping

tag: D
text: stop breathing temporarily while still sleeping
answer_key: D
explanation: D 以 irritation 做关键词定位至最后一句，说如果 irritation 太严重，睡着的人就会醒，按照正常的叙述顺序应该是先叙述 mild 的情况，前一句果然在说 coughing reflex 没产生 cough，而产生了 ceSSATion of breathing，呼吸停止的状况，所以答案是 D。C 与原文相反；B 是 severe 的时候才有的，A 没说.

question_stem: The word "considerable" (paragraph 3) meaning to
choices: tag: A
text: significant

tag: B
text: Steady

tag: C
text: Usual

tag: D
text: necessary
answer_key: A
explanation: A  considerable：可观的，相当的，A 是显著的，B 是稳定的，C 是通常的，D 是必要的。所以正确答案是 significant。

question_stem: The word "resume" in the passage (paragraph 3) is closest in meaning to
choices: tag: A
text: reduce

tag: B
text: stop

tag: C
text: Readjust

tag: D
text: restart
answer_key: D
explanation: A  resume: 重新开始，再继续。A 是减少，B 是停止，C 是重新调整，D 是重新开始。所以正确答案是 restart。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage (paragraph 6)? Incorrect choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: Because breathing is more shallow and irregular in REM than in NREM, less air is exchanged in REM.

tag: B
text: Breathing in NREM is less effective than breathing in REM because of irregular episodes of rapid breathing during NREM.

tag: C
text: Because breathing is more rapid in NREM sleep than in REM sleep, breathing often becomes shallow.

tag: D
text: Although REM has brief episodes of shallow breathing or lack of breathing, breathing is more rapid than in NREM.
answer_key: A
explanation: A 原句的主要逻辑就是因果逻辑，结果是 exchanged lower, 原因是 more irregular。在原因部分还使用了转折逻辑，和一个 with 结构的补充原因。而 A 选项将这个因果关系和几个关键内容都涵盖了，所以正确答案是 A。其他答案都没提到 exchange lower 这个主干，而且 B 把原文非主干的部分变成了主干；C 结果搞乱；D 逻辑关系错。