It has long been accepted that the Americas were colonized by amigrationof peoples from Asia, slowly traveling across a land bridge called Beringia (now the Bering Strait between northeastern Asia and Alaska) during the last Ice Age. The first watercrafttheoryabout themigrationwas that around 11,000-12,000 years ago there was an ice-freecorridorstretching from eastern Beringia to the areas of North America south of the great northern glaciers. It was the midcontinentalcorridorbetween twomassiveice sheets-the Laurentide to the west-that enabled the southwardmigration. But belief in this ice-freecorridorbegan tocrumblewhen paleoecologist Glen MacDonald demonstrated that some of the most importantradiocarbondates used to support theexistenceof an ice-freecorridorwere incorrect. He persuasively argued that such an ice-freecorridordid not exist until much later, when thecontinentalice began its finalretreat.

Support is growing for thealternativetheorythat people using watercraft, possibly skin boats, moved southward from Beringia along theGulfof Alaska and then southward along the Northwestcoastof North America possibly as early as 16,000 years ago. Thisroutewould have enabled humans to enter southern areas of the Americaspriorto themeltingof thecontinentalglaciers. Until the early 1970s,most archaeologists did notconsiderthecoasta possiblemigrationrouteinto the Americas because geologists originally believed that during the last Ice Age the entire NorthwestCoastwas covered byglacialice. It had been assumed that the ice extended westward from the Alaskan/Canadian mountains to the veryedgeof thecontinentalshelf, the flat, submerged part of thecontinentthat extends into the ocean. This would have created abarrierof ice extending from the Alaska Peninsula,throughtheGulfof Alaska and southward along the NorthwestCoastof north America to what is today thestateof Washington.

The mostinfluentialproponentof the coastalmigrationroutehas been Canadian archaeologist Knut Fladmark. He theorized that with the use of watercraft, peoplegraduallycolonized unglaciated refuges and areas along thecontinentalshelfexposedby the lower sea level. Fladmark’shypothesisreceivedadditionalsupport from the fact that the greatestdiversityin native American languages occurs along the westcoastof the Americas, suggesting that thisregionhas been settled the longest.

More recent geologic studies documented deglaciation and theexistenceof ice-free areasthroughoutmajor coastal areas of British Columbia, Canada, by 13,000 years ago. Research now indicates that sizable areas of southeastern Alaska along the innercontinentalshelf were not covered by ice toward the end of the last Ice Age. One study suggests that except for a 250-mile coastal area between southwestern British Columbia and WashingtonState, the NorthwestCoastof North America was largely free of ice byapproximately16,000 years ago. Vastareas along thecoastmay have been deglaciated beginning around 16,000 years ago, possibly providing a coastalcorridorfor the movement of plants, animals, and humans sometime between 13,000 and 14,000 years ago.

The coastalhypothesishas gained increasing support in recent years because the remains of large land animals, such ascaribouand brown bears, have been found in southeastern Alaska dating between 10,000 and 12,500 years ago. This is the time period in which most scientists formerly believed the area to beinhospitablefor humans. It has been suggested that if the environment werecapableof supportingbreedingpopulations of bears, there would have been enough food resources to support humans. Fladmark and other believe that the first humancolonizationof America occurred by boat along the NorthwestCoastduring the very late Ice Age, possibly as early as 14,000 years ago. The most recent geologicevidenceindicates that it may have been possible for people tocolonizeice-free regions along thecontinentalshelf that were stillexposedby the lower sea level between13,000 and 14,000 years ago.

The coastalhypothesissuggests aneconomybased onmarinemammalhunting, saltwater fishing gathering, and the use of watercraft. Because of thebarrierof ice to the east, thePacificOcean to the west, and populated areas to the north, there may have been a greaterimpetusfor people to move in a southerly direction.

Questions:
question_stem: According to paragraph 1, the theory that people first migrated to the Americans by way of an ice-free corridor was seriously called into question by
choices: tag: A
text: paleoecologist Glen MacDonald's argument that the original migration occurred much later than had previously been believed

tag: B
text: the demonstration that certain previously accepted radiocarbon dates were incorrect

tag: C
text: evidence that the continental ice began its final retreat much later than had previously been believed

tag: D
text: research showing that the ice-free corridor was not as long lasting as had been widely assumed
answer_key: B
explanation: B 以 ice-free corridor 做关键词定位至第二句和第四句，第二句只是单纯说这个理论是什么，问题问 called into question 遭到质疑为什么，所以答案应该在第四句。说这个理论 crumble 是因为 GM 先生发现 radiocarbon dates 是错的，所以答案 B。

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

tag: B
text: inflexibly

tag: C
text: convincingly

tag: D
text: carefully
answer_key: C
explanation: A persuasively: 有说服力的，令人信服的。A 是侵略地；B 是不屈地；C 是令人信服地；D 是认真地。所以 C 的 convincingly 正确。

question_stem: Paragraph 2 begins by presenting a theory and then goes on to
choices: tag: A
text: discuss why the theory was rapidly accepted but then rejected

tag: B
text: present the evidence on which the theory was based

tag: C
text: cite evidence that now shows that the theory is incorrect

tag: D
text: explain why the theory was not initially considered plausible
answer_key: D
explanation: D, 问题问先提出理论接着怎么了，所以看第二句。说这个路线能让人们在冰川融化之前进入美洲南部，所以这个是支持本段第一句内容的，而且后一句说直到70年代，人们才认同 coast 路线，也就是之前人们不认同这个理论，而后认为这个理论可能是对的。A 和 C 都不对；原文没说前面的理论是基于这个事实的，B 错，D 正确。

question_stem: The phrase “prior to” is closest in meaning to
choices: tag: A
text: before

tag: B
text: immediately after

tag: C
text: during

tag: D
text: in spite of
answer_key: A
explanation: prior to: 在……之前。A 是在…之前；B 是紧接；C 是在…期间；D 是尽管。想到 priority 优先，所以 A 对。对应原文:This route would have enabled humans to enter southern areas of the Americas prior to the melting of the continental glaciers.前句说从白令海沿阿拉斯加湾向南，整个都在说走水路的事情，MS 应该是冰化了之后，但原文特别强调进入美洲南部，也就是说人们通常是走冰川进入北部的，如果进入南部也是在冰川融化之后的话，就没有必要特别强调南部了。C 在冰川融化期间没有信息；D 尽管用的没必要。

question_stem: Paragraph 2 supports the idea that, before the 1970s, most archaeologists held which of the following views about the earliest people to reach the Americas?
choices: tag: A
text: They could not have sailed directly from Beringia to Alaska and then southward because, it was thought, glacial ice covered the entire coastal region.

tag: B
text: They were not aware that the climate would continue to become milder.

tag: C
text: They would have had no interest in migrating southward from Beringia until after the continental glaciers had begun to melt.

tag: D
text: They lacked the navigational skills and appropriate boats needed long-distance trips.
answer_key: A
explanation: A 以1970s 做关键词定位至第三句，70年代之前，人们都认为水路不可能，因为冰川覆盖了海面，所以 A 正确。B/C/D 都没说。

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 to leave out essential information.
choices: tag: A
text: Because this region has been settled the longest, it also displays the greatest diversity in Native American languages.

tag: B
text: Fladmark's hypothesis states that the west coast of the Americas has been settled longer than any other region.

tag: C
text: The fact that the greatest diversity of Native American languages occurs along the west coast of the Americans lends strength to Fradmark's hypothesis.

tag: D
text: According to Fladmark, Native American languages have survived the longest along the west coast of the Americas.
answer_key: C
explanation: C 原句的结构是 Fladmark 的 hypothesis 得到了 fact 的支持。C 说 fact lend strength to 他的 hypothesis，所以正确。A 的因果关系原文没有；原文说事实支持了 hypothesis，B 和 D 都说 Fladmark 说这个，偷换概念，都不对。

question_stem: The author's purpose in paragraph 4 is to
choices: tag: A
text: indicate that a number of recent geologic studies seem to provide support for the coastal hypothesis

tag: B
text: indicate that coastal and inland migrations may have happened simultaneously

tag: C
text: explain why humans may have reached America's northwest coast before animals and plants did

tag: D
text: show that the coastal hypothesis may explain how people first reached Alaska but it cannot explain how people reached areas like modern British Columbia and Washington State
answer_key: A
explanation: A 问整段的目的，所以看第一句。研究表明那时候加拿大海岸没有冰，所以是支持由海路到达美洲的 hypothesis，A 或者 D 可能对，但 D 后半句的 but 在原文没说，所以 A 正确。不放心的话往后再看看，第二句又是一个 research indicate blabla，所以 A 的 a number of studies 正确。

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

tag: B
text: Various

tag: C
text: Isolated

tag: D
text: Huge
answer_key: D
explanation: vast: 巨大的。A 是冻结的；B 是各种各样的；C 是孤立的，分离的；D 是巨大的。所以 D 的 huge 正确。对应原文:Vast areas along the coast may have been deglaciated beginning around 16,000 years ago, possibly providing a coastal corridor for the movement of plants, animals, and humans sometime between 13,000 and 14,000 years ago. 原文说沿岸的怎么样的地区没有冰了，给人和动物提供了迁徙的通道，只有大片地方都没有冰，才能形成通道。既然没有冰，A 的 frozen 一定错；B 多样的错，因为原文没说很多地区；都形成通道了，C 隔绝错。

question_stem: According to paragraph 5, the discovery of the remains of large land animals supports the coastal hypothesis by providing evidence that
choices: tag: A
text: humans were changing their hunting techniques to adapt to coastal rather than inland environments

tag: B
text: animals had migrated from the inland to the coasts, an indication that a midcontinental ice-free corridor was actually implausible

tag: C
text: humans probably would have been able to find enough resources along the coastal corridor

tag: D
text: the continental shelf was still exposed by lower sea levels during the period when the southward migration of people began
answer_key: C
explanation: C 以 remains of large land animal 做关键词定位至第一句，但这句明显只是问题的重复，所以往后看，下一句说 inhospitable，再下一句说如果熊有吃的人也有，所以答案 C 正确。其他都没说。

question_stem: The word “inhospitable” in the passage is closest in meaning to
choices: tag: A
text: not familiar

tag: B
text: not suitable

tag: C
text: not dangerous

tag: D
text: not reachable
answer_key: B
explanation: inhospitable: 不适于居住的，不好客的。A 是不熟悉；B 是不适合；C 是不危险；D 是不可获得。所以 B 不适合正确。对应原文:This is the time period in which most scientists formerly believed the area to be inhospitable for humans.下一句说如果熊有吃的人也有，就是人能活下来，inhospitable 所在的这句因为有 formerly believed 就说明人们之前认为不能活下来，所以 C 不危险反了；A 和 D 都没说。

question_stem: According to paragraph 5, the most recent geologic research provides support for a first colonization of America dating as far back as
choices: tag: A
text: 16,000 years ago

tag: B
text: 14,000 years ago

tag: C
text: 12,500 years ago

tag: D
text: 10,000 years ago
answer_key: B
explanation: 可以根据 most recent geologic research 定位到原文最后一句：The most recent geologic evidence indicates that it may have been possible for people to colonize ice-free regions along the continental shelf that were still exposed by the lower sea level between 13,000 and 14,000 years ago.这里说了在13,000和14,000年之间，B 正确。这一段一共就三个地方提到了时间（第一句，最后两句），快速扫过也可以迅速找到答案。

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

tag: B
text: protection

tag: C
text: possibility

tag: D
text: incentive
answer_key: D
explanation: impetus: 推动力，刺激。A 是机会；B 是保护；C 是可能性；D 是动机，刺激。所以 D 的 incentive 正确。对应原文:Ocean to the west, and populated areas to the north, there may have been a greater impetus for people to move in a southerly direction. 原句说由于东西北三个方向都有障碍没法迁徙，所以人们往南飞行的什么更大。如果单纯带进去，A 的 chance 和 C 的 possibility 都对，但这两个词的意思非常接近，所以都不对。protection 完全不靠谱。