Earth’s surface is not made up of a single sheet of rock that forms acrustbut rather a number of “tectonicplates” that fit closely, like the pieces of a giantjigsawpuzzle. Some plates carry islands or continents, others form the seafloor. All are slowly moving because the platesfloaton a denser semi-liquidmantle, thelayerbetween thecrustand Earth’score. The plates have edges that arespreading ridges(where two plates are moving apart and new seafloor is being created),subduction zones(where two platescollideand one plungesbeneaththe other), ortransformfaults(where two plates neitherconvergenordivergebut merely move past one another). It is at the boundaries between plates that most of Earth’s volcanism and earthquakeactivityoccur.

Generally speaking, the interiors of plates are geologically uneventful. However, there are exceptions. Aglanceat a map of thePacificOcean reveals that there are many islands far out at sea that are actually volcanoes----many no longer active, some overgrown with coral----that originated fromactivityat points in theinteriorof thePacificPlatethat forms thePacificseafloor.

How canvolcanicactivityoccurso far from aplateboundary?

The Hawaiian islands provide a very instructive answer. Like many other island groups, they form achain. The Hawaiian IslandsChainextends northwest from the island of Hawaii. In the 1840s AmericangeologistJames Daly observed that the different Hawaii islandsseemto share asimilargeologicevolutionbut are progressively more eroded, andthereforeprobable older, toward the northwest. Then in 1963, in the early days of thedevelopmentof thetheoryofplatetectonics. Canadian geophysicist Tuzo Wilson realized that this age progression could result if the islands were formed on a surfaceplatemoving over a fixedvolcanicsourcein theinterior. Wilson suggested that the longchainof volcanoes stretching northwest from Hawaii issimplythe surface expression of a long-livedvolcanicsourcelocatedbeneaththetectonicplatein themantle. Today’s most northwest island would have been the first to form. They as theplatemoved slowly northwest, newvolcanicislands would have forms as theplatemoved over thevolcanicsource. The most recent island, Hawaii, would be at the end of thechainand is now over thevolcanicsource.

Although this idea was not immediately accepted, the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently activevolcano, just as Daly had suggested. Wilson’sanalysisof thesedatais now a central part ofplatetectonics. Most volcanoes thatoccurin the interiors of plates are believed to be produced bymantleplumes, columns ofmoltenrock that rise from deepwithinthemantle. Avolcanoremains an active “hotspot” as long as it is over the plume. The plumes apparentlyoriginateat great depths, perhaps as deep as theboundarybetween thecoreand themantle, and many have been active for a very long time. The oldest volcanoes in the Hawaii hot-spottrailhave ages close to 80 million years. Other islands, including Tahiti andEasterIslands in thepacific,Reunionand Mauritius in the India Ocean, and indeed most of the large islands in the world’s oceans, owe theirexistencetomantleplumes.

Theoceanicvolcanicislands and their hot-spot trails are thus especially useful forgeologistbecause theyrecordthe past locations of theplateover a fixedsource. Theythereforepermitthereconstructionof theprocessof seafloor spreading, andconsequentlyof the geography of continents and of ocean basins in the past. For example,giventhecurrentpositionof thePacificPlate, Hawaii is above thePacificOcean hotspot. So thepositionof ThePacificPlate50 million years ago can bedeterminedby moving it such that a 50-million-year-oldvolcanoin the hot-spottrailsits at the location of Hawaii today. However because the ocean basins really are short-lived features on geologic timesscale,reconstructionthe world’s geography by backtrackingalongthe hot-spottrailworks only for the last 5 percent or so of geologic time.

Questions:
question_stem: The author mentions “spreading ridges”, “subduction zones”, and “transform faults”in order to
choices: tag: A
text: illustrate that the boundaries of tectonic plates are neat, thin lines

tag: B
text: explain why some tectonic plates carry islands or continents while others form the seafloor

tag: C
text: explain the complex nature of the edges of tectonic plates

tag: D
text: provide examples of areas of tectonic plates where little geologic action occurs
answer_key: C
explanation: C 原文这部分介绍了各种不同的 edges 的现象，并做了详细的解释，前面也说到 plate 的组成就像是 jigsaw puzzle，从两处可以看出应该是要体现其复杂性。A 与原文矛盾，原文并没有对 B 做出解释，D 原文给出的是 geologic action 常发的地方，而不是 little ~ occurs。

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

tag: B
text: form

tag: C
text: rise

tag: D
text: move closer
answer_key: D
explanation: D converge: 聚集，靠拢。A 选项为扩张，B 选项为形成，C 选项为升起，D 选项为移得更紧。从词意上来选择的话，D 选项更为适合。

question_stem: Which of the sentences below best expresses the essential information in the highlighted sentence in the passage paragraph 2? Incorrect choices change the meaning in important ways or leave out essential information
choices: tag: A
text: Volcanic activity is responsible for the formation of the Pacific seafloor in the interior of the Pacific Plate.

tag: B
text: Many volcanoes in the Pacific Ocean are no longer active and have become islands that support coral.

tag: C
text: There are many islands in the Pacific Ocean that originated as volcanoes in the interior of the Pacific Plate.

tag: D
text: The map of the Pacific Ocean reveals fewer volcanic islands than there truly are because many are no longer active and some are completely overgrown with coral.
answer_key: C
explanation: C  这句话的破折号之内的插入部分可以忽略不看，是非主要逻辑。而句子主干部分主要说的是很多岛屿事实上是火山，后面说了起源。只有 C 选项将主干内容涵盖了。A 选项很原句的意思差距甚远。B 选项的内容并不是原句的核心内容，将核心内容遗漏；D 选项的 fewer than 这样的比较关系在原句没有体现，且原句也没有因果关系。

question_stem: The word “instructive”in the passage (paragraph 3) is closest in meaning to
choices: tag: A
text: clear

tag: B
text: detailed

tag: C
text: informative

tag: D
text: familiar
answer_key: C
explanation: C instructive: 有益的，有启发性的，教育性的。 A 是清楚的，B 是细节的，D 是熟悉的。只有 C 是有益的，教育性的，意思吻合。

question_stem: The word “eroded”in the passage(paragraph 3)is closest in meaning to
choices: tag: A
text: worn down

tag: B
text: scattered

tag: C
text: developed

tag: D
text: deserted
answer_key: A
explanation: A  这句话说不同的岛屿看起来经历了相似的演变过程，但有些随着时间推移被更……，所以可能更古老。那么岛屿如果经历的时间更长应该会被海水“侵蚀”的更厉害。所以答案选 A，worn down 磨损。 B 是分散的，C 是发达的，成熟的；D 是被遗弃的。

question_stem: In paragraph 3, what is the relationship between the scientific contribution of James Daly and Tuzo Wilson?
choices: tag: A
text: Wilson provided an explanation for the observations made by Daly.

tag: B
text: Wilson challenged the theory proposed by Daly.

tag: C
text: Wilson found numerous examples of island chains that supported Daly’s theory.

tag: D
text: Wilson popularized the explanation of volcanic island formation formulated by Daly.
answer_key: A
explanation: A 根据两个科学家的名字进行定位。从 then in 1963这一句可以了解到两者关系，说在板块理论刚开始发展的时期，Tuzo Wilson 发现…那么肯定是使板块理论进一步发展了。所以 B 不对。而 C 虽然逻辑关系对，但文中只给了夏威夷岛一个例子。所以 C 不选。D 说使解释流行，之前 daly 只是给了理论，并没解释，所以不对。而 A 既符合逻辑关系，也对 wilson 的描写是正确的。选 A。

question_stem: Why does the author provide the information that “the dating of lavas in the Hawaii (and other) chains showed that their ages increase away from the presently active volcano”?
choices: tag: A
text: To point out differences between the Hawaii island chain and other volcanic island chains

tag: B
text: To question the idea that all the islands in an island chain have been formed by volcanic activity

tag: C
text: To explain why Wilson hypothesis was initially difficult to accept

tag: D
text: To provide evidence in support of Daly’s and Wilson’s ideas about how the Hawaii islands were formed
answer_key: D
explanation: D 句内修饰：just as Daly had suggested。通过这个句内修饰，说明了给出的这个事实，是为了证明 Daly 在前一段所说的理论是正确的。也可以从前半句话的转折看出，之前没有什么人接受他的理论，转折之后当然是论证他的理论是有依据的。和 D 选项呼应。

question_stem: According to paragraph 4, which of the following is true of mantle plumes
choices: tag: A
text: They exist close to the surface of tectonic plates.

tag: B
text: They cause most of the volcanic activity that occurs in the interiors of plates.

tag: C
text: They are rarely active for long period of time.

tag: D
text: They get increasingly older away from the present hot spots.
answer_key: B
explanation: B  根据 mantle plumes 定位，可定位到第二句,就说了它是导致板块内部火山爆发的原因，往后读可以看到它首先是起源于很深的地方，其次活动时间很长。因此 A，C，D 都不对。所以正确答案 B。

question_stem: According to paragraph 5, volcanic islands help geologists to
choices: tag: A
text: reconstruct past geography

tag: B
text: detect changes in mantle plumes

tag: C
text: measure the rigidity of tectonic plates

tag: D
text: explain why the seafloor spreads
answer_key: A
explanation: A  定位到这一段的第二句。D 选项虽然也对，但是 A 可以包括 D，所以选 A。

question_stem: What can be inferred about the Pacific Plate from paragraph 5?
choices: tag: A
text: The hot spots on the Pacific Plate are much older than the ones located on the other tectonic plates.

tag: B
text: Most of the volcanic sources beneath the Pacific Plate have become extinct.

tag: C
text: The Pacific Plate has moved a distance equal to the length of the Hawaiian Island chain in the past 50 million years.

tag: D
text: The Pacific Plate is located above fewer mantle plumes than other plates are.
answer_key: C
explanation: 定位到 for example，定位句几乎就是选项 C 的原义转换啦。A，B，D 原文都没提到。

question_stem: The word “current”in the passage (paragraph 5) is closest in meaning to
choices: tag: A
text: original

tag: B
text: ideal

tag: C
text: relative

tag: D
text: present
answer_key: D
explanation: D current: 现在的，当前的。A 是原始的，B 是理想的，C 是相对的，D 是现在的。根据词意，D 选项正确。

question_stem: According to paragraph 5, why are geologists unable to trace back the entire geologic of continents from hot-spot trails?
choices: tag: A
text: Hot spots have existed for only about 5 percent of geologic time.

tag: B
text: Hawaii did not exist 50 millions years ago.

tag: C
text: Oceanic basins that contained old hot-spot trails disappeared a long time ago.

tag: D
text: Hot-spot trails can be reconstructed only for island chains.
answer_key: C
explanation: C  定位到最后一句。说不能追踪到整个变化过程是因为海洋盆地的变化相对比较快。