In the middle of the nineteenthcentury, Louis Agassiz, one of the first scientists to study glaciers, immigrated to the United States from Switzerland and became a professor at Harvard University, where he continued his studies ingeologyand other sciences. For his research, Agassiz visited many places in the northern parts of Europe and North America, from the mountains ofScandinaviaand New England to the rolling hills of the American Midwest. In all thesediverseregions, Agassiz saw signs ofglacialerosionandsedimentation. In flat plains country, he saw moraines (accumulationsof earth andlooserock that form at the edges of glaciers) that reminded him of theterminalmoraines found at the end ofvalleyglaciers in the Alps. The heterogeneousmaterialof thedrift(sand,clay, and rocks deposited there) convinced him of itsglacialorigin.

The areas covered by thismaterialwere sovastthat the ice that deposited it must have been acontinentalglacierlarger than Greenland orAntarctica. Eventually, Agassiz and others convinced geologists and the general public that a greatcontinentalglaciationhad extended thepolarice caps far into regions that now enjoytemperateclimates. For the first time, people began to talk about ice ages. It was alsoapparentthat theglaciationoccurred in therelativelyrecent past because thedriftwassoft, likefreshlydepositedsediment. We now know the age of theglaciationaccurately from radiometric dating of the carbon-14 in logs buried in thedrift. Thedriftof the lastglaciationwas deposited during one of the most recent epochs of geologic time, thePleistocene, which lasted from 1.8 million to 10,000 years ago. Alongthe eastcoastof the United States, the southernmostadvanceof this ice is recorded by theenormoussand anddriftdeposits of theterminalmoraines that form Long Island andCapeCod.

It soon becameclearthat there weremultipleglacialages during thePleistocene, with warmerinterglacialintervals between them. As geologists mappedglacialdeposits in the late nineteenthcentury, they becameawarethat there were several layers ofdrift, thelowerones corresponding to earlier ice ages. Between the older layers ofglacialmaterialwere well-developed soils containing fossils of warm-climate plants. These soils wereevidencethat the glaciers retreated as theclimatewarmed. By the early part of the twentiethcentury, scientists believed that fourdistinctglaciations had affected North America and Europe during thePleistoceneepoch.

This idea was modified in the late twentiethcentury, when geologists and oceanographers examiningoceanicsedimentfoundfossilevidenceof warming and cooling of the oceans. Ocean sediments presented a much more complete geologicrecordof thePleistocenethancontinentalglacialdeposits did. The fossils buried inPleistoceneand earlier ocean sediments were of foraminifera—small, single-celledmarineorganisms thatsecreteshells ofcalciumcarbonate, or calcite. These shells differ in theirproportionof ordinaryoxygen(oxygen-16) and the heavyoxygenisotope(oxygen-18). Theratioof oxygen-16 to oxygen-18 found in the calcite of a foraminifer'sshelldepends on thetemperatureof the water in which theorganismlived. Different ratios in the shells preserved in various layers ofsedimentrevealthetemperaturechanges in the oceans during thePleistoceneepoch.

Isotopicanalysisof shells allowed geologists tomeasureanotherglacialeffect. They couldtracethe growth andshrinkageofcontinentalglaciers,evenin parts of the ocean where there may have been no great change intemperature—around theequator, for example. Theoxygenisotoperatioof the ocean changes as a greatdealof water is withdrawn from it byevaporationand is precipitated as snow to formglacialice. During glaciations, the lighter oxygen-16 has a greatertendencytoevaporatefrom the ocean surface than the heavier oxygen-18 does. Thus, more of the heavyisotopeis left behind in the ocean and absorbed bymarineorganisms. From thisanalysisofmarinesediments, geologists have learned that there were many shorter, moreregularcycles ofglaciationand deglaciation than geologists had recognized from theglacialdriftof the continents alone.

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

tag: B
text: pieces

tag: C
text: types

tag: D
text: deposits
answer_key: D
explanation: D accumulation: 沉积，聚集。A 是符号，标志；B 是匹，块；C 是种类；D 是沉积物。所以答案是 D 的 deposit。

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

tag: B
text: varied

tag: C
text: familiar

tag: D
text: layered
answer_key: B
explanation: B heterogeneous: 异质的，由不同成分形成的。A 是剩下的；B 是各式各样的；C 是常见的；D 是分层的，层状的。所以正确答案是 B。

question_stem: According to paragraph 1, what persuaded Louis Agassiz that glaciation in the past had been widespread?
choices: tag: A
text: Geologic differences between mountain valleys and flat plains

tag: B
text: The presence of similar glacial material in many different regions

tag: C
text: Geologic research on mountain glaciers in the Alps

tag: D
text: Evidence of regional differences in the drift caused by glacial erosion
answer_key: B
explanation: B, 人名多次出现，所以单纯使用人名作为关键词不好，配合 glacial 冰川做关键词。总共出现两次次，第一次是第一句介绍这个人，与答案无关；第二次是说这个人在不同的地方都发现了冰蚀和沉积痕迹，所以答案是 B。D 的 regional difference 说反；A 的 geologic difference 原文没说，C 答非所问。

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

tag: B
text: resemble

tag: C
text: expect

tag: D
text: dominate
answer_key: A
explanation: A enjoy: 享受，经历。A 是经历；B 是类似；C 是期望，预料；D 是控制，支配。所以 A 的 experience 正确。

question_stem: It can be inferred from paragraph 2 that Agassiz and other geologists of his time were not able to determine
choices: tag: A
text: which geographic regions had been covered with ice sheets in the last ice age

tag: B
text: the exact dates at which drifts had been deposited during the last ice age

tag: C
text: the exact composition of the drifts laid during the last ice age

tag: D
text: how far south along the east coast of the United States the ice had advanced during the last ice age
answer_key: B
explanation: B 此题关键词不好找，所以排除法较好。A 的 last ice age 做关键词定位至倒数第二句，说 last glaciation 的沉积时间，往下看就看到美国东海岸，所以沉积的地区是能确定的，不选；B 的 date 做关键词定位至倒数第三句，说现在知道了冰川的年龄，根据时间对比，也就是以前不知道，恰恰是答案，所以 B 正确；C 的 composition 成分做关键词定位至最后一句，说 drift 是 morain，所以成分是知道的；D 的 how far south 做关键词定位至第二句的 temperate climate，所以 D 也是错的。

question_stem: According to paragraph 3, what did geologists conclude as a result of finding well-developed soils containing warm-climate plant fossils between layers of glacial drift?
choices: tag: A
text: There had been only one warm period before the Pleistocene epoch.

tag: B
text: There had been multiple periods of mild weather between ice ages.

tag: C
text: Several glacial periods occurred after the Pleistocene epoch.

tag: D
text: Some earlier epochs were warmer thant the Pleistocene.
answer_key: B
explanation: B 以 warm-climate plant fossils 做关键词定位至第三句，但这句没说结论是什么，往下看，下句说这些土壤是冰川后退的证据，所以正确答案是 B。注意 C 的 several glacial periods 不对，原文说的是有若干个暖器。

question_stem: According to paragraph 3 and 4, scientists modified their theory about the exact number of glaciations because of evidence obtained from
choices: tag: A
text: ocean sediments

tag: B
text: interglacial soils

tag: C
text: glacial deposits

tag: D
text: air samples
answer_key: A
explanation: A 以 modified their theory 做关键词定位至第一句，说改变了 idea 的原因是他们看了 oceanic sediment 里面的化石，所以证据是来自 ocean sediment 的，答案是 A。

question_stem: The word “reveal” in the passage is closest in meaning to
choices: tag: A
text: result from

tag: B
text: vary with

tag: C
text: show

tag: D
text: preserve
answer_key: C
explanation: C reveal: 揭示，揭开。A 是结果；B 是随…而变化；C 是展现，解释；D 是保存。所以 C 的 show 正确。

question_stem: According to paragraph 4, scientists use foraminifera shells to learn about Pleistocene ocean conditions by
choices: tag: A
text: measuring the amount of calcium carbonate present in the shells

tag: B
text: determining the proportion of shell in each layer of sediment

tag: C
text: comparing shells deposited during the Pleistocene with those buried earlier

tag: D
text: calculating the relative quantity of two oxygen isotopes in the calcite
answer_key: D
explanation: D 以 Pleistocene 和 foraminifer 做关键词定位至第三句，但这句话只说了有种叫做有孔虫的海洋微体古生物，没说能用来干嘛，所以往下看，下句说能够计算有孔虫壳体中两种氧同位素的比值，进而反映海水的温度，所以答案是 D，计算氧同位素的比值。

question_stem: In can be inferred from paragraph 5 that foraminifera fossil shells containing calcite with high percentages of oxygen-16 were deposited at times when
choices: tag: A
text: polar ice extended as far as equatorial regions of land and sea

tag: B
text: extensive glaciation was not occurring

tag: C
text: there were no great increases in ocean temperature

tag: D
text: there was heavy snowfall on continental glaciers
answer_key: B
explanation: B 以 oxygen-16做关键词定位至第四句，说在冰期时候，氧16更容易蒸发，使得海水中的氧18就多，反过来氧16就多，也就是说，问题问的应该是暖期，所以答案是 B，不存在广泛的冰川。ACD 三项说的都是冷期，所以都说反了。

question_stem: In paragraph 5, why does the author include the information that the “oxygen isotope ratio of the ocean changes as a great deal of water is withdrawn from it by evaporation and is precipitated as snow to form glacial ice” ?
choices: tag: A
text: To explain how scientists were able to calculate how frequently the continental ice sheets expanded and contracted

tag: B
text: To explain how scientists have determined that there was no great change in ocean temperatures at the equator during past glaciations

tag: C
text: To provide evidence that oxygen-16 has a greater tendency to evaporate than does oxygen-18

tag: D
text: To suggest that equatorial marine organisms absorb more heavy isotopes than do marine organisms elsewhere
answer_key: A
explanation: A 修辞目的题，修辞点所在句子整个就是一个例子，所以往前看，前一句说科学家们能够分析冰川的进退，所以答案是 A。B 是前句的一个细节，C 和 D 没说。

question_stem: According to the passage, when did scientists begin to realize that more than one ice age had occurred ?
choices: tag: A
text: In the mid nineteenth century

tag: B
text: In the late nineteenth century

tag: C
text: In the early twentieth century

tag: D
text: In the late twentieth century
answer_key: B
explanation: B，此题答案简单，只有两个时间，而且是要找全文的，所以使用排除法。在第三段最后一句找到二十世纪，往附近看，本段第二句说十九世纪晚期人们发现有很多层沉积物，下部的沉积物对应早期的冰期，也就是发现有多次冰期出现，所以正确的时间应该是在十九世纪晚期，所以答案是 B。