ThePacificOcean accounts for one-third of Earth’s surface and half of the world’s

ocean area.

It has about 25,000 islands, of which about 7,500 areoceanic, beingrelativelyfar from acontinentalshore. The greatmajorityof allPacificislands were

bornbarrenof life: hard,dense,volcanicrock pimples on the sea's surface. New

Zealand is thechiefexception; it is among thecontinentalislands of the westernPacific, together with Fiji, the Solomons, and others to the west.

Life arrived on most other islands byaccidentor bydrift. Some plants arrived byairtransport; seeds carried in thedigestivetracts of birdsaccountfor nearly 40 percent of Hawaii's early plants. The first invaders were either creatures that couldfloatwell enough, inairor water, to cross stretches of ocean, or those whose seeds couldsurviveavoyagein some bird'sgut. At times oflowersealevel, land bridges linked, or nearly linked, many islands in the far westernPacific, so somespeciescolonized these islands without beingnotablygood floaters or stowaways. In the easternPacific(EasterIsland, for example) only the best floaters and travelers arrived and survived. Consequently, the western islands have far morespeciesand far greaterbiodiversitythan do the eastern islands of Polynesia. Mammals found it hard to get anywhere in the islandPacific; only bats and rats successfully colonized east of NewGuinea. Almost allspeciesderivefrom Asia; the earlyPacificwas an Asian lake, with only a tinyproportionofspeciesfrom the Americas. As a rule of thumb, the further from Indonesia, the more impoverished the plant and animal life and, inconsequence, the lessstableandresilientin the face ofdisturbance. This attenuation is strong for landspecies, less strong formarinespecies, and nonexistent foroceanicbirds, althoughfairlystrong for land birds.

Pacificecosystems evolved inrelative(but differential) isolation from thecontinentalcrucibles of biologicalevolution. This meant opportunities for speciation: thedevelopmentof newspeciesoccupyingecologicalniches that elsewhere were already filled. The finches described by thenaturalistCharles Darwin on the Galapagos Islands—birds that divided into differentspecies, eachspecializedfor a narrowniche—are theclassicexample. On islands that had no mammals, reptiles and birds took their place. Thus the Galapagos havegianttortoises, and New Zealand once hadgiantbirds that functioned more or less like browsing orgrazingmammals. Throughoutmost of thePacific, thepaucityofgrazinganimals meant that plants developed no defenses, such as spines,poisonouschemicals, or bitterness. The remoter islands had a very highproportionofendemism—that is，ofspeciesthat existed only there. In the case of Hawaii, as many as 99 percent of thespecieswereendemic. All this led to a certain biologicalvulnerabilityamong theterrestrialislandspecies, should they ever beobligedtocompetefornichespacewith the winners of the moreintensecontinentalcompetitions forsurvival. Thisvulnerabilityincreased toward the east and toward the remoter corners of thePacificalongagradientdefinedchieflyby thedegreeof isolation.

Asecondsourceofvulnerability, perhaps more decisive, arose from the arrival of humankind in thePacific. Island animals evolved with no experience of the ways of humankind, or indeed of any largeterrestrialpredators. As a result, they had no immunities to predators or the effects of humanaction. Pacificanimals were often unwary and easyprey. At theextreme, again the Galapagos, Darwin found many birds almost tame, so naively trusting that they would allow him to getwithinarm’sreach. Pacificplants had little experience with fire, because natural fires were veryrare, except in a few places. Thus few plants were well adapted to fire, and most provedvulnerableto it. Incontrast,continentalspeciesthat had evolved in the presence of humankind, or in places where natural fire is much morecommon, couldrecovereasily after burns, and some couldflourishas a result of fire. In short,Pacificecosystems were different fromcontinentalones onaccountof their isolation. They were well adapted to their circumstances but veryvulnerabletoalieninvasionand humanimpact.

Questions:
question_stem: The main purpose of paragraph 1 is to
choices: tag: A
text: introduce the major ideas that will be discussed in the passage

tag: B
text: explain how the Pacific Ocean differs from other oceans

tag: C
text: impress on the audience the large number of islands the Pacific Ocean contains

tag: D
text: provide relevant geographical background to the topic of the passage
answer_key: D
explanation: 题干提问“第1段主要目的”，建议完成后面题目、对全文内容有宏观把控后再做第1题，可直接得知第1段为后文提供了相关的地理背景，故选 D。

question_stem: Which of the sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important ways orleave out essential information.
choices: tag: A
text: When sea levels were low, land bridges that connected many islands in the far western Pacific were able to form.

tag: B
text: Good floaters and stowaways were able to take advantage of land bridges at times of lower sea level.

tag: C
text: Some species that could not invade in the usual way did so by crossing land bridges when sea levels dropped.

tag: D
text: Colonizing the islands of the far western Pacific was accomplished by some species because they were good floaters or stowaways.
answer_key: C
explanation: 分析高亮句主干：海平面低时，路桥连接岛屿，因此物种无需漂浮物就可以定居于此。强调核心“物种定居”，故选 C，主干 some species did so（did so = invaded = clonized）符合原文高亮句主干。A 的 land bridges 不是高亮句讨论主体，B 的 good floaters and stowaways 及 D 的 because they were good floaters or stowaways 不符合高亮句 without being notably good floaters or stowaways。

question_stem: What can be inferred from the discussion about “bats”and“rats” in relation to other mammals?
choices: tag: A
text: Small mammals such as bats and rats could not travel as far as larger mammals could.

tag: B
text: Bats and rats had advantages in crossing oceans that other mammals lacked.

tag: C
text: Unlike other mammals, bats and rats originated in the Americas rather than Asia.

tag: D
text: After colonizing a Pacific island, bats and rats adapted better to the ecosystems than other mammals did.
answer_key: B
explanation: 题干提问“从 bats、rats 与其他哺乳动物关系的讨论中可推断出”，定位高亮句后第3句：哺乳动物发现在太平洋岛屿上很难到达任何地方，只有蝙蝠和老鼠成功地定居在新几内亚东部。再结合前文 best floaters and travelers arrived and survived 得知 bats and rats 可以 floate and travel，即 B 的 cross oceans，故选 B。A 的 could not travel 与原文说反，C 的 originated in the Americas、D 的 adapted better to 均未提及。

question_stem: According to paragraph 2, why were mammals not common in the island Pacific?
choices: tag: A
text: It was nearly impossible for most mammals to travel from island to island.

tag: B
text: Mammals tried to colonize the islands at a time when the land bridges were widely separated.

tag: C
text: Because mammals are native to the Americas, they could not survive in the alien climate of the island Pacific.

tag: D
text: The early plants of the island Pacific did not provide suitable food for mammals.
answer_key: A
explanation: 题干提问“为什么哺乳动物在太平洋岛屿不常见”，与第3题部分重叠，定位 Mammals found it hard to get anywhere in the island Pacific，哺乳动物发现在太平洋岛屿上很难到达任何地方，故选 A。B 的 try to colonize，C 的 native to Americas，D 的 suitable food 均未提及。

question_stem: The author mentions "giant tortoises" and "giant birds" in paragraph 3 in order to
choices: tag: A
text: describe some unusual varieties of animals that evolved on the oceanic Pacific islands

tag: B
text: contrast the diversity of animal life on the Galapagos and New Zealand to that of most other islands

tag: C
text: illustrate that non-mammals evolved to fill niches that might otherwise have been filled by mammals

tag: D
text: argue that Galapagos animals and New Zealand animals occupied similar ecological niche
answer_key: C
explanation: 题干提问“作者在第3段提及 giant tortoises 和 giant birds 目的是”，定位第3段第5句 Thus the Galapagos have giant tortoises, and New Zealand once had giant birds that functioned more or less like browsing or grazing mammals。因 giant tortoises、giant birds 出现在题干中，为文中例子，giant tortoises 为 reptiles，giant birds 为 birds，则举例说明 On islands that had no mammals, reptiles and birds took their place 及 This meant opportunities for speciation: the development of new species occupying ecological niches that elsewhere were already filled.，故选 C。ABD 不能与中心论点对应。

question_stem: Which of the following can be inferred from paragraph 3 about why plants in Pacific ecosystems did not develop defenses?
choices: tag: A
text: The fragile plants were not strong enough to support thick spines.

tag: B
text: The absence of mammals that typically feed on plants meant that defenses were unnecessary.

tag: C
text: Poisonous chemicals that might affect the plants were not present.

tag: D
text: The plants were able to occupy niches in areas where there were no birds or tortoises.
answer_key: B
explanation: 题干提问“为什么太平洋生态系统中的植物没有防御能力”，对应第6句 Throughout most of the Pacific, the paucity of grazing animals meant that plants developed no defenses, such as spines, poisonous chemicals, or bitterness，由 the paucity of grazing animals 得知食草动物的稀缺是植物没有防御能力的原因所在，故选 B。A 的 not strong enough to support thick spines，C 的 poisonous chemicals were not present，D 的 occupy niches in areas where there were no birds or tortoises 均未提及。

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

tag: B
text: domesticated

tag: C
text: careless

tag: D
text: confident
answer_key: B
explanation: tame （1）adj. （兽、鸟等）驯服的；枯燥乏味的；（人）温顺的；（2）v. 驯化，驯服，使易于控制。文中取 adj.“（兽、鸟等）驯服的”之意，与 domesticated 同义，故选 B。

question_stem: In paragraph 4, the author mentions fire in relation to plants in order to make which of the following points?
choices: tag: A
text: Natural fires generally harmed but did not destroy plants in continental ecosystems.

tag: B
text: Natural fires in the Pacific islands were difficult to control and caused the destruction of many plants.

tag: C
text: Naturally occurring fires can be much more destructive of plant life than fires started by humans.

tag: D
text: Plants on the Pacific islands had not evolved any mechanisms for coping with fire.
answer_key: D
explanation: 题干提问“作者提到与植物有关的火灾是为了表明什么观点”，根据 fire in relation to plants 定位第4段第5-6句 Pacific plants had little experience with fire, because natural fires were very rare, except in a few places. Thus few plants were well adapted to fire, and most proved vulnerable to it. 太平洋植物很少着火，因为除了少数地方，自然火灾很少见。 因此，很少有植物能很好地适应火灾，并且大多数都容易燃烧。故选 D。ABC 不能与论点信息对应。