Survivaland successfulreproductionusuallyrequirethe activities of animals to be coordinated withpredictableevents around them. Consequently, the timing and rhythms of biological functions must closelymatchperiodicevents like thesolarday, the tides, thelunarcycle, and the seasons. The relations between animalactivityand these periods, particularly for the daily rhythms, have been of suchinterestand importance that a hugeamountof work has been done on them and thespecialresearchfieldof chronobiology has emerged. Normally, theconstantlychanging levels of an animal'sactivity—sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones, for example—are well coordinated withenvironmentalrhythms, but the key question is whether the animal'sscheduleis driven byexternalcues, such as sunrise orsunset, or isinsteaddependent somehow oninternaltimers that themselvesgeneratethe observed biological rhythms. Almost universally, biologists accept the idea that all eukaryotes (acategorythat includes most organisms exceptbacteriaand certainalgae) haveinternalclocks. By isolating organisms completely fromexternalperiodiccues, biologists learned that organisms haveinternalclocks. Forinstance, apparently normal daily periods of biologicalactivitywere maintained for about a week by thefungusNeurospora when it wasintentionallyisolatedfrom all geophysical timing cues while orbiting in aspaceshuttle. Thecontinuationof biological rhythms in anorganismwithoutexternalcues attests to its having aninternalclock.

When crayfish are kept continuously in the dark,evenfor four to five months, theircompoundeyes continue toadjuston a dailyschedulefor daytime and nighttimevision. Horseshoe crabs kept in the dark continuously for a year were found tomaintainapersistentrhythmof brainactivitythat similarly adapts their eyes on a dailyschedulefor bright or for weak light. Like almost all daily cycles of animals deprived ofenvironmentalcues, those measured for the horseshoe crabs in these conditions were not exactly 24 hours. Such arhythmwhose period isapproximately—but not exactly—a day is called circadian. For differentindividualhorseshoe crabs, the circadian period ranged from 22.2 to 25.5 hours. Aparticularanimal typically maintains its owncharacteristiccycledurationwith great precision for many days. Indeed,stabilityof the biological clock's period is one of itsmajorfeatures,evenwhen theorganism's environment is subjected toconsiderablechanges in factors, such astemperature, that would be expected toaffectbiologicalactivitystrongly. Furtherevidenceforpersistentinternalrhythms appears when the usualexternalcycles are shifted—either experimentally or by rapid east-west travel over great distances. Typically, the animal's daily internally generatedcycleofactivitycontinues without change. As a result, its activities are shiftedrelativeto theexternalcycleof the new environment. The disorienting effects of this mismatch betweenexternaltime cues andinternalschedules maypersist, like our jet lag, for several days or weeks until certain cues such as the daylight/darknesscyclereset theorganism's clock tosynchronizewith the dailyrhythmof the new environment.

Animals need naturalperiodicsignals like sunrise tomaintainacyclewhose period is precisely 24 hours.Such anexternalcuenot only

coordinates an animal's daily rhythms withparticularfeatures of thelocalsolarday but also—because itnormallydoes so day after day-seems to keep

theinternalclock's period close to that of   Earth'srotation.Yet despite thissynchronizationof the period of theinternalcycle, the animal's timer

itself continues to have its owngeneticallybuilt-in period close to, but different from, 24 hours.Without theexternalcue, thedifferenceaccumulates and so

the internally regulated activities of the biological daydriftcontinuously, like the tides, in relation to thesolarday.Thisdrifthas been studied extensively in

many animals and in biological activities ranging from the hatching of fruit fly eggs to wheel running by squirrels.Light has a predominating influence insettingthe clock.Evena fifteen-minute burst of light inotherwisesustaineddarkness can reset an animal's circadianrhythm.Normally,internalrhythms are kept in step byregularenvironmentalcycles.Forinstance, if ahomingpigeonis tonavigatewith its Suncompass, its clock must be properly set by cues provided by the daylight/darknesscycle. Such anexternalcuenot only

coordinates an animal's daily rhythms withparticularfeatures of thelocalsolarday but also—because itnormallydoes so day after day-seems to keep

theinternalclock's period close to that of   Earth'srotation. Yet despite thissynchronizationof the period of theinternalcycle, the animal's timer

itself continues to have its owngeneticallybuilt-in period close to, but different from, 24 hours. Without theexternalcue, thedifferenceaccumulates and so

the internally regulated activities of the biological daydriftcontinuously, like the tides, in relation to thesolarday. Thisdrifthas been studied extensively in

many animals and in biological activities ranging from the hatching of fruit fly eggs to wheel running by squirrels. Light has a predominating influence insettingthe clock. Evena fifteen-minute burst of light inotherwisesustaineddarkness can reset an animal's circadianrhythm. Normally,internalrhythms are kept in step byregularenvironmentalcycles. Forinstance, if ahomingpigeonis tonavigatewith its Suncompass, its clock must be properly set by cues provided by the daylight/darknesscycle.

Questions:
question_stem: The word “Consequently” in the passage is closest in meaning to
choices: tag: A
text: Therefore

tag: B
text: Additionally

tag: C
text: Nevertheless

tag: D
text: Moreover
answer_key: A
explanation: A consequently: 因此，所以。A 是因此；B 是额外的；C 是然而；D 是而且，此外。所以 A 的 therefore 正确。

question_stem: In paragraph 1, the experiment on the fungus Neurospora is mentioned to illustrate
choices: tag: A
text: the existence of weekly periods of activity as well as daily ones

tag: B
text: the finding of evidence that organisms have internal clocks

tag: C
text: the effect of space on the internal clocks of organisms

tag: D
text: the isolation of one part of an organism's cycle for study
answer_key: B
explanation: 功能目的题，N 所在的这句话就是一个例子，而且这句话一开始就有一个 for example，说明这句话是前一句话的例子，往前看： By isolating organisms completely from external periodic cues, biologists learned that organisms have internal clocks. 把生物同外部条件完全隔绝之后，我们就可以发现生物的内部节律，所以答案是 B。

question_stem: According to paragraph 1, all the following are generally assumed to be true EXCEPT:
choices: tag: A
text: It is important for animals' daily activities to be coordinated with recurring events in their environment.

tag: B
text: Eukaryotes have internal clocks.

tag: C
text: The relationship between biological function and environmental cycles is a topic of intense research.

tag: D
text: Animals' daily rhythms are more dependent on external cues than on internal clocks.
answer_key: D
explanation: EXCEPT 题，排除法。A 的 activities 和 coordinate 做关键词定位至第一句，正确，不选；B 的 E 做关键词定位至倒数第四句，明确指出有 internal，所以正确，不选；C 的 intense research 做关键词定位至第三句，正确，不选；D 的比较原文没说，错，选。

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

tag: B
text: strong

tag: C
text: enduring

tag: D
text: predicted
answer_key: C
explanation: C persistent: 持续的。A 是调整过的；B 是强壮的；C 是持续的；D 是预测的。所以 C 的 enduring 正确。

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: Stability, a feature of the biological clock's period, depends on changeable factors such as temperature.

tag: B
text: A major feature of the biological clock is that its period does not change despite significant changes in the environment.

tag: C
text: A factor such as temperature is an important feature in the establishment of the biological clock's period.

tag: D
text: Biological activity is not strongly affected by changes in temperature.
answer_key: B
explanation: B 原句的主要逻辑是让步，结构就是：稳定性是主要的 feature 之一，即使环境会遭受很多因素的变化。其中的 such as 这种举例的插入成分，完全可以忽略不看。B 与之完全一致，是正确答案。A 的 depend 纯属编造；C 和 D 都完全改变了原文的主干，错。

question_stem: According to paragraph 2, which of the following is true about the circadian periods of animals deprived of environmental cues?
choices: tag: A
text: They have the same length as the daily activity cycles of animals that are not deprived of such cues.

tag: B
text: They can vary significantly from day to day.

tag: C
text: They are not the same for all members of a single species.

tag: D
text: They become longer over time.
answer_key: C
explanation: 以 circadian 做关键词定位至第四句，因为这句话一开始就是一个 such，说明可能和上句有联系，读下这两句，说如果没有 environmental cue，那么马蹄蟹的 period 就不是24小时，这个24小时就叫 circadian，接着文章又说可能是22.2 to 25.5小时，所以答案是 C，同物种的 circadian 也不一样。此题易错选 A，因为前文特别强调没有外部环境因素的时候 circadian 不是24小时，所以不 same，A 错。

question_stem: According to paragraph 2, what will an animal experience when its internal rhythms no longer correspond with the daily cycle of the environment?
choices: tag: A
text: Disorientation

tag: B
text: Change in period of the internal rhythms

tag: C
text: Reversal of day and night activities increased

tag: D
text: Sensitivity to environmental factors
answer_key: A
explanation: 以 cycle of the environment 做关键词定位至倒数第二句，这句之前说生物的内部节律不变，接着说生物的活动不得不因为新环境而发生改变，然后就出现了 mismatch，后句中的 disorientation 就是正确答案。B 与原文相反，C 和 D 没说.

question_stem: In paragraph 2, the author provides evidence for the role of biological clocks by
choices: tag: A
text: listing the daily activities of an animal's cycle: sleeping, feeding, moving, reproducing, metabolizing, and producing enzymes and hormones

tag: B
text: describing the process of establishing the period of a biological clock

tag: C
text: presenting cases in which an animal's daily schedule remained stable despite lack of environmental cues

tag: D
text: contrasting animals whose daily schedules fluctuate with those of animals whose schedules are constant
answer_key: C
explanation: C 问作者是怎么给出 biological clock 的作用的，不好定位找答案，使用排除法。A 说列出了动物的周期性活动，只是单纯列出活动无法起到说明生物钟的作用，太肤浅，不对；原文没有描述生物钟的形成，B 错；C 对应原文倒数第五句(句子简化题那句话)，说没有外部环境条件生物钟仍然可以起作用，说明生物钟起的作用重要，不依靠其他，所以 C 是答案；D 的两者对比原文没说，不选。

question_stem: The word "duration" in the passage is closest in meaning to
choices: tag: A
text: length

tag: B
text: feature

tag: C
text: process

tag: D
text: repetition
answer_key: A
explanation: A  duration: 时长。A 是长度，B 是特征；C 是过程；D 是重复。所以 A 的 length 正确。

question_stem: In paragraph 2, why does the author mention that the period for different horseshoe crabs ranges from 22.2 to 25.5 hours?
choices: tag: A
text: To illustrate that an animal's internal clock seldom has a 24-hour cycle

tag: B
text: To argue that different horseshoe crabs will shift from daytime to nighttime vision at different times

tag: C
text: To illustrate the approximate range of the circadian rhythm of all animals

tag: D
text: To support the idea that external cues are the only factors affecting an animal's periodic behavior
answer_key: A
explanation: 修辞目的题，先看下数字所在的这句，说不同的马蹄蟹的 circadian 在22.2到25.5小时之间，明显只是个例子。前一句说像这种大致24小时却不是准确的24小时的节律叫做 circadian，也就是说后面这句说的就是 circadian 不是准确的24小时的一个例子，所以答案是 A。B 的 shift from daytime to nighttime 没说；C 和 D 都太绝对而且原文没说.

question_stem: The word “it” in the passage refers to
choices: tag: A
text: an external cue such as sunrise

tag: B
text: the daily rhythm of an animal

tag: C
text: the local solar day

tag: D
text: a cycle whose period is precisely 24 hours
answer_key: A
explanation: A 指代，往前找，找名词，因为有 but also，前面就一定有 not only，而且 not only 与 but also 共用同一主语，所以 not only 之前的主语就是这道题的答案 A。

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

tag: B
text: uninterrupted

tag: C
text: natural

tag: D
text: periodic
answer_key: B
explanation: B，sustained: 持续的，持久的。A 是强烈的；B 是不间断的；sustained 就是维持的，连续的，所以 B 的不间断的正确。