To South Americans, robins are birds that fly north everyspring. To North Americans, the robinssimplyvacationin the south each winter. Furthermore, they fly to veryspecificplaces in South America and will often come back to the same trees in North American yards the followingspring. The question is not why they would leave the cold of winter so much as how they find their way around. The question perplexed people for years, until, in the 1950s, a German scientist named Gustave Kramer provided some answers and, in theprocess, raised new questions.

Kramer initiated important new kinds of research regarding how animals orient andnavigate. Orientationissimplyfacing in the right direction;navigationinvolves finding ones way from point A to point B.

Early in his research, Kramer found that cagedmigratorybirds became very restless at about the time they wouldnormallyhave begunmigrationin the wild. Furthermore, he noticed that as they fluttered around in the cage, they often launched themselves in the direction of their normalmigratoryroute. He then set up experiments with caged starlings and found that theirorientationwas, in fact, in thepropermigratorydirection except when the sky was overcast, at which times there was nocleardirection to their restless movements. Kramer surmised,therefore, that they were orienting according to thepositionof the Sun. To test this idea, he blocked their view of the Sun and used mirrors to change itsapparentposition. He found that under these circumstances, the birds oriented withrespectto the new "Sun." They seemed to be using the Sun as acompasstodeterminedirection. At the time, this idea seemed preposterous. How could a birdnavigateby the Sun when some of us lose our way with road maps? Obviously, more testing was in order.

So, in another set of experiments, Kramer putidenticalfood boxes around the cage, with food in only one of the boxes. The boxes werestationary, and the one containing food was always at the same point of thecompass. However, itspositionwithrespectto the surroundings could be changed by revolving either theinnercage containing the birds or the outer walls, which served as the background. As long as the birds could see the Sun, no matter how their surroundings were altered, they went directly to the correct food box. whether the box appeared in front of the right wall or the left wall, they showed no signs ofconfusion. On overcast days, however, the birds weredisorientedand had trouble locating their food box.

In experimenting withartificialsuns, Kramer made another interesting discovery. If theartificialSun remainedstationary, the birds wouldshifttheir direction withrespectto it at arateof about 15 degrees per hour, the Sun'srateof movementacrossthe sky. Apparently, the birds were assuming that the "Sun" they saw was moving at thatrate. When the real Sun wasvisible, however, the birds maintained aconstantdirection as it movedacrossthe sky. In other words, they were able tocompensatefor the Sun's movement. This meant that somesortof biological clock was operating-and a verypreciseclock at that.

What about birds thatmigrateat night? Perhaps theynavigateby the night sky. To test the idea, caged night-migrating birds were placed on the floor of a planetarium during theirmigratoryperiod. A planetarium isessentiallya theater with a domelike ceiling onto which a night sky can be projected for any night of the year. When the planetarium sky matched the sky outside, the birds fluttered in the direction of their normalmigration. But when thedomewas rotated, the birds changed their direction tomatchtheartificialsky. The results clearly indicated that the birds were orienting according to the stars.

There is accumulatingevidenceindicating that birdsnavigateby using a widevarietyofenvironmentalcues. Other areas underinvestigationinclude magnetism, landmarks, coastlines, sonar, andevensmells. The studies arecomplicatedby the fact that thedataare sometimescontradictoryand the mechanisms apparently change from time to time. Furthermore, onesensoryabilitymay back up another.

Questions:
question_stem: Which of the following can be inferred about bird migration from paragraph 1?
choices: tag: A
text: Birds will take the most direct migratory route to their new habitat.

tag: B
text: The purpose of migration is to join with larger groups of birds.

tag: C
text: Bird migration generally involves moving back and forth between north and south.

tag: D
text: The destination of birds' migration can change from year to year.
answer_key: C
explanation: C 这道题的关键词明显不是很好找，而且排除法的话答案又太长，所以看本段的开头，说南美的鸟春天飞去北方，而北美的鸟冬天飞去南方，所以答案是 C，between north and south，其他的选项都没有相关信息。

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

tag: B
text: interested

tag: C
text: puzzled

tag: D
text: occupied
answer_key: C
explanation: C  perplex: 困惑。A 是几百；B 是使…感兴趣；C 是迷惑；Dshi 占据。所以 C 的 puzzle 正确。 对应原文 The question perplexed people for years, until, in the 1950s, a German scientist named Gustave Kramer provided some answers and, in the process, raised new questions.   原句说这个问题 perflex 人们很多年，直到五十年代才给出一些 answer，也就是之前都没有 answer，所以答案是困扰。既然已经找到答案了，所以 A 的打败一定不对；只是 B 感兴趣肯定不行，没有问题的话后面也没必要说给出答案了；D 的 occupy 是占领，只是使人们有问题也不够，所以 D 也不对。

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: Experiments revealed that caged starlings displayed a lack of directional sense and restless movements.

tag: B
text: Experiments revealed that caged starlings were unable to orient themselves in the direction of their normal migratory route.

tag: C
text: Experiments revealed that the restless movement of caged starlings had no clear direction.

tag: D
text: Experiments revealed that caged starlings' orientation was accurate unless the weather was overcast.
answer_key: D
explanation: D, 原文的结构是这个人做了一个实验并且有了结果。但四个答案都没说做实验，所以只关注实验结果就可以，说这些鸟的 orientation 除了 overcast 的时候都是对的。ABC 都和原句矛盾，原句强调的是基本都是有方向感的。

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

tag: B
text: inadequate

tag: C
text: limited

tag: D
text: creative
answer_key: A
explanation: A preposterous: 荒谬的，可笑的。A 是难以置信的；B 是不充足的；C 是有限的；D 是创造性的。想到 pre 表向前，post 表向后，能想出这个意思，所以 unbelievable 不值得相信的，难以置信的正确。

question_stem: According to paragraph 3, why did Kramer use mirrors to change the apparent position of the Sun?
choices: tag: A
text: To test the effect of light on the birds' restlessness

tag: B
text: To test whether birds were using the Sun to navigate

tag: C
text: To simulate the shifting of light the birds would encounter along their regular migratory route

tag: D
text: To cause the birds to migrate at a different time than they would in the wild
answer_key: B
explanation: B 以人名和 mirror 做关键词定位至第四、五句，说这个人认为鸟是用太阳导航的，为了验证这个观点，这个人用镜子做了一个实验，所以做这个实验的目的就是验证鸟是不是用太阳导航的，答案是 B，其他都没说。

question_stem: According to paragraph 3, when do caged starlings become restless?
choices: tag: A
text: When the weather is overcast

tag: B
text: When they are unable to identify their normal migratory route

tag: C
text: When their normal time for migration arrives

tag: D
text: When mirrors are used to change the apparent position of the Sun
answer_key: C
explanation: 以 restless 定位到做第一句：Early in his research, Kramer found that caged migratory birds became very restless at about the time they would normally have begun migration in the wild.这句话中明确说了在他们要开始迁徙的时候变得 restless，和 C 选项对应。注意此题容易误选 A，很多同学读到了第三句中的 restless。但原文说 overcast 的时候鸟的 migratory orientation 就没方向，跟 restless 无关。B 跟 A 在同一句，都与问题无关，所以错；D 在第四句，也跟问题无关，不选。

question_stem: Which of the following can be inferred from paragraph 4 about Kramer's reason for filling one food box and leaving the rest empty?
choices: tag: A
text: He believed the birds would eat food from only one box.

tag: B
text: He wanted to see whether the Sun alone controlled the birds' ability to navigate toward the box with food.

tag: C
text: He thought that if all the boxes contained food, this would distract the birds from following their migratory route.

tag: D
text: He needed to test whether the birds preferred having the food at any particular point of the compass.
answer_key: B
explanation: B 以 food box 做关键词定位至本段倒数两句，说不管盒子怎么放鸟都不会晕，但阴天的时候就会晕，结合前文一直在说的 K 做的实验，说明鸟是用太阳识别方向的，所以答案是 B，而且这段一开始就说 another set of experiments 所以可以往前看，前一段也在说鸟用太阳辨别方向，所以这段说的只是一系列试验中的一个，其他没说。

question_stem: According to paragraph 5, how did the birds fly when the real Sun was visible?
choices: tag: A
text: They kept the direction of their flight constant.

tag: B
text: They changed the direction of their flight at a rate of 15 degrees per hour.

tag: C
text: They kept flying toward the Sun.

tag: D
text: They flew in the same direction as the birds that were seeing the artificial Sun.
answer_key: A
explanation: A 以 real sun 做关键词定位至倒数第二句，说当真的太阳能看到的时候，鸟的飞行方向不变。A 说 flying direction 是 constant 持续的，完全改写，是正确答案。C 虽然说了飞行方向不变，但没说鸟是朝着太阳飞的；B 的15度和 D 的与人造太阳时飞行的方向一致都没说。

question_stem: The experiment described in paragraph 5 caused Kramer to conclude that birds possess a biological clock because
choices: tag: A
text: when birds navigate they are able to compensate for the changing position of the Sun in the sky

tag: B
text: birds innate bearings keep them oriented in a direction that is within 15 degrees of the Sun's direction

tag: C
text: birds' migration is triggered by natural environmental cues, such as the position of the Sun

tag: D
text: birds shift their direction at a rate of 15 degrees per hour whether the Sun is visible or not
answer_key: A
explanation: A 以 biological clock 做关键词定位至最后一句，但这句一开始就说这意味着 blabla，所以往前看，说这些鸟保持飞行方向不变是因为他们能弥补太阳位置变化引起的变化，所以 A 是答案，B 和 D 都说了，但不能成为有 biological clock 的原因，而 C 完全没说。

question_stem: According to paragraph 6, how did the birds navigate in the planetarium's nighttime environment?
choices: tag: A
text: By waiting for the dome to stop rotating

tag: B
text: By their position on the planetarium floor

tag: C
text: By orienting themselves to the stars in the artificial night sky

tag: D
text: By navigating randomly until they found the correct orientation
answer_key: C
explanation: C 以 planetarium 做关键词定位至第三句，但这句只在说一个现象，所以往下看，当 planetarium 的 sky 与外面的一样，鸟就正常迁徙；不一样的时候鸟就根据人造的 sky 定位，最后得出是用星星定位的，所以 C 是答案，其他的完全没说。

question_stem: Which of the following best describes the author's presentation of information in the passage?
choices: tag: A
text: A number of experiments are described to support the idea that birds use the Sun and the night sky to navigate.

tag: B
text: The author uses logic to show that the biological clock in birds is inaccurate.

tag: C
text: A structured argument about the importance of internal versus external cues for navigation is presented.

tag: D
text: The opposing points of view about bird migration are clarified through the study of contrasting experiments.
answer_key: A
explanation: A : 问通篇文章，需要看每段首句修辞目的题，问整段的，所以看首句，前几段都在说白天鸟用太阳定位，后面说鸟是靠 night sky 定位的所以综合起来，答案是 A，分别叙述鸟在日间和夜间的定位方法。

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

tag: B
text: increasing

tag: C
text: convincing

tag: D
text: extensive
answer_key: B
explanation: B，accumulating: 逐渐增加的。A 是新的，B 是增加的，C 是令人信服的；D 是广泛的，大量的。所以 B 的 increasing 正确。 对应原文 There is accumulating evidence indicating that birds navigate by using a wide variety of environmental cues. 本句说一系列的 cue，所以是越来越多的，new 不对，因为如果是新的或者是 extensive 广泛的话后句不会说 other；同理后句说 under investigation，所以应该是不确定，convincing 错。