Paleontologists have argued for a long time that thedemiseof the dinosaurs was caused byclimaticalterations associated with slow changes in the positions of continents and seas resulting fromplatetectonics. Off and onthroughouttheCretaceous(the last period of theMesozoicera, during which dinosaurs flourished), largeshallowseas coveredextensiveareas of the continents. Datafromdiversesources, including geochemicalevidencepreserved in seafloor sediments,indicatethat the LateCretaceousclimatewas milder than today’s. The days were not too hot, nor the nights too cold. The summers were not too warm, nor the winters toofrigid. Theshallowseas on the continents probably buffered thetemperatureof the nearbyair, keeping itrelativelyconstant.

At the end of theCretaceous, the geologicalrecordshows that these seaways retreated from the continents back into themajorocean basins. No one knows why. Over a period of about 100,000 years, while the seas pulled back, climates around the world becamedramaticallymore extreme: warmer days, cooler nights; hotter summers, colder winters. Perhaps dinosaurs could nottoleratetheseextremetemperaturechanges and becameextinct.

If true, though, why did cold-blooded animals such as snakes, lizards, turtles, and crocodilessurvivethe freezing winters and torrid summers? These animals are at themercyof theclimatetomaintaina livable bodytemperature. It’s hard to understand why they would not be affected, whereas dinosaurs were left too crippled to cope, especially if, as some scientists believe, dinosaurs were warm-blooded. Critics also point out that theshallowseaways had retreated from andadvancedon the continentsnumeroustimes during theMesozoic, so why did the dinosaurssurvivetheclimaticchanges associated with the earlier fluctuations but not with this one? Althoughinitiallyappealing, thehypothesisof a simpleclimaticchange related to sea levels isinsufficientto explain all thedata.

Dissatisfaction withconventionalexplanations fordinosaurextinctions led to a surprisingobservationthat, in turn, has suggested a newhypothesis. Many plants and animals disappearabruptlyfrom thefossilrecordas one moves from layers of rock documenting the end of theCretaceousup into rocks representing the beginning of the Cenozoic (theeraafter theMesozoic). Between the lastlayerofCretaceousrock and the firstlayerof Cenozoic rock, there is often a thinlayerofclay. Scientists felt that they could get an idea of how long the extinctions took by determining how long it took todepositthis one centimeter ofclayand they thought they coulddeterminethe time it took todeposittheclayby determining theamountof theelementiridium(Ir) it contained.

Ir has not beencommonat Earth’s since the very beginning of theplanet’shistory.Because it usually exists in ametallicstate,

it was preferentially incorporated in Earth’scoreas theplanetcooled and consolidated.Ir is found in high concentrations in some meteorites,

in which thesolarsystem’soriginalchemicalcompositionis preserved.Eventoday,microscopicmeteorites continually bombard Earth, falling on both land and sea.By measuring how many of these meteorites fall to Earth over agivenperiod of time, scientists canestimatehow long it might have taken todepositthe observedamountof Ir in theboundaryclay.These calculations suggest that a period of about one million years would have been required.However, otherreliableevidencesuggests that thedepositionof theboundaryclaycould not

have taken one million years.So the unusually highconcentrationof Ir seems torequireaspecialexplanation. Because it usually exists in ametallicstate,

it was preferentially incorporated in Earth’scoreas theplanetcooled and consolidated. Ir is found in high concentrations in some meteorites,

in which thesolarsystem’soriginalchemicalcompositionis preserved. Eventoday,microscopicmeteorites continually bombard Earth, falling on both land and sea. By measuring how many of these meteorites fall to Earth over agivenperiod of time, scientists canestimatehow long it might have taken todepositthe observedamountof Ir in theboundaryclay. These calculations suggest that a period of about one million years would have been required. However, otherreliableevidencesuggests that thedepositionof theboundaryclaycould not

have taken one million years. So the unusually highconcentrationof Ir seems torequireaspecialexplanation.

In view of these facts, scientists hypothesized that a single largeasteroid, about 10 to 15 kilometersacross, collided with Earth, and the resulting fallout created theboundaryclay. Their calculations show that theimpactkicked up a dust cloud that cut off sunlight for several months, inhibitingphotosynthesisin plants; decreased surface temperatures on continents to below freezing; causedextremeepisodes ofacidrain; andsignificantlyraised long-term global temperaturesthroughthe greenhouse effect. This disruption of foodchainandclimatewould have eradicated the dinosaurs and other organisms in less than fifty years.

Questions:
question_stem: According to paragraph 1, which of the following is true of the Late Cretaceous climate?
choices: tag: A
text: Summers were very warm and winters were very cold.

tag: B
text: Shallow seas on the continents caused frequent temperature changes.

tag: C
text: The climate was very similar to today’s climate.

tag: D
text: The climate did not change dramatically from season to season.
answer_key: D
explanation: 以 Late Cretaceous climate 做关键词定位至倒数第四句：

Data from diverse sources, including geochemical evidence preserved in seafloor sediments, indicate that the Late Cretaceous climate was milder than today’s. The days were not too hot, nor the nights too cold. 

说比现在更温和，白天不太热，晚上不太冷。所以 D 是答案。A 与倒数第二句矛盾，错；B 与最后一句相反，错；C 说跟现在 similar，跟原文的 milder 矛盾。

question_stem: Which of the following reasons is suggested in paragraph 2 for the extinction of the dinosaurs?
choices: tag: A
text: Changes in the lengths of the days and nights during the late Cretaceous period

tag: B
text: Droughts caused by the movement of seaways back into the oceans

tag: C
text: The change from mild to severe climates during the Late Cretaceous period

tag: D
text: An extreme decrease in the average yearly temperature over 10,ooo years
answer_key: C
explanation: C 以 extinction of the dinosaurs 做关键词定位至最后一句，原句说不能忍受这些极端温度的恐龙灭绝了，因为有个 these，所以网上看一句，说冬天很冷夏天很热，所以 C 是答案。A 和 B 都没说；D 的 decrease 没说。

question_stem: Why does the author mention the survival of “snakes, lizards, turtles, and crocodiles” in paragraph 3?
choices: tag: A
text: To argue that dinosaurs may have become extinct because they were not cold-blooded animals

tag: B
text: To question the adequacy of the hypothesis that climatic change related to sea levels caused the extinction of the dinosaurs

tag: C
text: To present examples of animals that could maintain a livable body temperature more easily than dinosaurs

tag: D
text: To support a hypothesis that these animals were not as sensitive to climate changes in the Cretaceous period as they are today
answer_key: B
explanation: B, 先读所在句，说为什么诸如 blabla 之类的动物能耐得住这种极端气候呢，而且这句一开始就来了个 if true，所以应该是作者在质疑上端所提出的结论的正确性，而且最后一句是本段的中心句，说将气候变化的原因归于 sea level 是不对的，所以答案是 B。

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

tag: B
text: move

tag: C
text: continue

tag: D
text: compete
answer_key: A
explanation: cope: 应付。A 是适应；B 是移动；C 是继续；D 是竞争。所以 A 的 adapt 适应正确。对应原文 ：It’s hard to understand why they would not be affected, whereas dinosaurs were left too crippled to cope, especially if, as some scientists believe, dinosaurs were warm-blooded.原文说很难理解为什么其他动物没被影响，而恐龙特别弱以至于不能怎么样。转折说明恐龙被影响了，所以应该是难易度过之类的意思，所以 A 和 C 靠谱，至于为什么不是 C，只能靠认识了。

question_stem: According to paragraph 3, which of the following is true of changes in climate before the Cretaceous period and the effect of these changes on dinosaurs?
choices: tag: A
text: Climate changes associated with the movement of seaways before the Cretaceous period did not cause dinosaurs to become extinct.

tag: B
text: Changes in climate before the Cretaceous period caused severe fluctuations in sea level, resulting in the extinction of the dinosaurs.

tag: C
text: Frequent changes in climate before the Cretaceous period made dinosaurs better able to maintain a livable body temperature.

tag: D
text: Before the Cretaceous period there were few changes in climate, and dinosaurs flourished.
answer_key: A
explanation: A 以 before the Cretaceous period 做关键词，但注意原文中与之对应的是倒数第二句的 earlier，问为什么恐龙在之前的动荡中生存了下来而这次没有，所以 A 是答案，说之前的变化没有引起恐龙灭绝。B 说反了；C 的恐龙 better able to maintain 原文没说；D 的恐龙 flourish 繁盛没说。

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

tag: B
text: retreats

tag: C
text: periods

tag: D
text: variations
answer_key: D
explanation: fluctuation: 波动，震荡，变化。A 是极端条件；B 是撤退；C 是周期；D 是变化。所以 D 的 variation 正确。对应原文：Critics also point out that the shallow seaways had retreated from and advanced on the continents numerous times during the Mesozoic, so why did the dinosaurs survive the climatic changes associated with the earlier fluctuations but not with this one?原句说为什么恐龙熬过了其他的气候变化而这次没能成功熬过来，fluctuation 和 one 都指 change；而且之前还说海道从陆上进进退退，这也是变化，所以 variation 正确；A 极端 B 撤退 C 周期都不对。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? In correct choices change the meaning in important ways or leave out essential information.
choices: tag: A
text: The fossil record suggests that there was an abrupt extinction of many plants and animals at the end of the Mesozoic era.

tag: B
text: Few fossils of the Mesozoic era have survived in the rocks that mark the end of the Cretaceous.

tag: C
text: Fossils from the Cretaceous period of the Mesozoic up to the beginning of the Cenozoic era have been removed from the layers of rock that surrounded them.

tag: D
text: Plants and animals from the Mesozoic era were unable to survive in the Cenozoic era.
answer_key: A
explanation: A 原文的结构是 blabla 的时候 plants and animals 从化石中突然消失了。A 正确；B 错，原文没说 few fossil；C 把非主干部分变成了主干，而且 remove 也没说；D 选项缺了原文里化石这个很重要的信息，错。

question_stem: In paragraph 4, all the following questions are answered EXCEPT:
choices: tag: A
text: Why is there a layer of clay between the rocks of the Cretaceous and Cenozoic?

tag: B
text: Why were scientists interested in determining how long it took to deposit the layer of clay at the end of the Cretaceous?

tag: C
text: What was the effect of the surprising observation scientists made?

tag: D
text: Why did scientists want more information about the dinosaur extinctions at the end of the Cretaceous?
answer_key: A
explanation: A 的 layer of clay 定位至倒数第二句：
Between the last layer of Cretaceous rock and the first layer of Cenozoic rock, there is often a thin layer of clay. 
但原文只是说有 layer，没说为什么有，所以 A 的问题没得到回答，选；

B 的 how long 和 deposit 定位至最后一句，正确，不选：
Scientists felt that they could get an idea of how long the extinctions took by determining how long it took to deposit this one centimeter of clay and they thought they could determine the time it took to deposit the clay by determining the amount of the element iridium (lr) it contained.

C 的 surprising observation 对应第一句和第二句：
Dissatisfaction with conventional explanations for dinosaur extinctions led to a surprising observation that, in turn, has suggested a new hypothesis.
C 直接对应，正确，不选；D 也对应第一句，说对传统理论的不满，导致了一个 observation 和相应的假说，所以 D 正确，不选。

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

tag: B
text: strike

tag: C
text: pass

tag: D
text: circle
answer_key: B
explanation: bombard: 轰击，炮轰，撞击。A 是接近；B 是击打；C 是经过，通过；D 是旋转；环形。所以 B 的 strike 正确。对应原文：Even today, microscopic meteorites continually bombard Earth, falling on both land and sea.原句说直到今天，那些显微级的小星体还在怎么样地球，落在陆地上和海里。后半句话是对前半句的的补充说明，意思应该一致。既然是 falling on，那么 A 和 B 都有可能正确。而 bomb 的意思是轰炸，炸弹，那么正确的就是 B 了。

question_stem: Paragraph 5 implies that a special explanation of Ir in the boundary clay is needed because
choices: tag: A
text: the Ir in microscopic meteorites reaching Earth during the Cretaceous period would have been incorporated into Earth’s core

tag: B
text: the Ir in the boundary clay was deposited much more than a million years ago

tag: C
text: the concentration of Ir in the boundary clay is higher than in microscopic meteorites

tag: D
text: the amount of Ir in the boundary clay is too great to have come from microscopic meteorites during the time the boundary clay was deposited
answer_key: D
explanation: D 显然 ir 和 boundary clay 都不可以用来定位，用 special explanation 定位到最后一句，但这句知识重复了题干，而 so 就告诉你要往前看。倒数第三四句话说：根据一定时期内落入地球陨星的数量可以推断出积累这么多铹需要多长时间，据此推测需要几百万年；而倒数第二句则说：但可靠的证据表明并没有经历这么长的时间。因此可以推测出，如此高含量的铹需要进一步解释，与 D 选项对应。

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

tag: B
text: disturbance

tag: C
text: modification

tag: D
text: disappearance
answer_key: B
explanation: disruption: 打断，干扰。A 是枯竭，耗尽；B 是干扰，骚乱；C 是修改；D 是消失。所以 B 的 disturbance 正确。对应原文：This disruption of food chain and climate would have eradicated the dinosaurs and other organisms in less than fifty years.原句一开始就一个 this，说明与前文有关，前面是一个很长的句子，说一个 impact 弄出了一大堆 dust cloud，这些 cloud 做了 cut off 了阳光，阻碍了光合作用，又做了很多 blabla 事儿。所以一定是不好的词，C 的 modification 改变中性，不对；A 用尽和 D 消失都说食物链没了，但原文没说食物链消失了，而且两个词意思过于相近也不选。

question_stem: Paragraph 6 mentions all of the following effects of the hypothesized asteroid collision EXCEPT
choices: tag: A
text: a large dust cloud that blocked sunlight

tag: B
text: an immediate drop in the surface temperatures of the continents

tag: C
text: an extreme decrease in rainfall on the continents

tag: D
text: a long-term increase in global temperatures
answer_key: C
explanation: C，EXCEPT 题，排除法。A 的 dust cloud，B 的 drop in the surface temperatures 和 D 的 increase in global temperatures 都能定位至第二句，都正确，不选；C 的 rainfall 原文没说，错，选。