When it comes tophysiology, the leatherbackturtleis, in some ways, more like a reptilian whale than aturtle. It swims farther into the cold of the northern and southern oceans than any other seaturtle, and it deals with the chilly waters in a wayuniqueamongreptiles.

A warm-bloodedturtlemayseemto be acontradictionin terms. Nonetheless, an adult leatherback canmaintaina bodytemperatureof between 25 and 26°C (77-79°F) in seawater that is only 8°C (46.4°F). Accomplishing thisfeatrequires adaptations both togenerateheat in theturtle’s body and to keep it from escaping into the surrounding waters. Leatherbacks apparently do notgenerateinternalheat the way we do, or the way birds do, as aby-productof cellularmetabolism. A leatherback may be able to pick up some body heat by basking at the surface; its dark, almost black body color may help it toabsorbsolarradiation. However, most of itsinternalheat comes from theactionof its muscles.

Leatherbacks keep their body heat in three different ways. The first, and simplest, is size. The bigger the animal is, thelowerits surface-to-volumeratio; for every ounce of bodymass, there is proportionately less surfacethroughwhich heat canescape. An adult leatherback is twice the size of the biggest cheloniid sea turtles and willthereforetake longer to cool off. Maintaining a high bodytemperaturethroughsheerbulkis called gigantothermy. It works for elephants, for whales, and, perhaps, it worked for many of the larger dinosaurs. It apparently works, in a smaller way, for some other sea turtles. Large loggerhead and green turtles canmaintaintheir bodytemperatureat adegreeor two above that of the surrounding water, and gigantothermy is probably the way they do it. Muscularactivityhelps, too, and an actively swimming greenturtlemay be 7°C (12.6°F) warmer than the waters it swimsthrough.

Gigantothermy, though, would not be enough to keep a leatherback warm in cold northern waters. It is not enough for whales, whichsupplementit with a thicklayerof insulatingblubber(fat). Leatherbacks do not haveblubber, but they do have a reptilian equivalent: thick, oil-saturated skin, with alayeroffibrous, fattytissuejustbeneathit. Insulationprotects the leatherback everywhere but on its head and flippers. Because the flippers arecomparativelythin and blade-like, they are the one part of the leatherback that is likely to becomechilled. There is not much that theturtlecan do about this without compromising the aerodynamicshapeof theflipper. The problem is that as blood flowsthroughtheturtle’s flippers, it risks losing enough heat tolowerthe animal’s central bodytemperaturewhen it returns. Thesolutionis to allow the flippers to cool down without drawing heat away from the rest of theturtle’s body. The leatherback accomplishes this by arranging the blood vessels in the base of itsflipperinto acountercurrentexchangesystem.

In acountercurrentexchangesystem, the blood vessels carrying cooled blood from the flippers run close enough to the blood vessels carrying warm blood from the body to pick up some heat from the warmer blood vessels; thus, the heat is transferred from the outgoing to the ingoing vessels before it reaches theflipperitself. This is the same arrangement found in an old-fashioned steam radiator, in which the coiled pipes pass heat back and forth as water coursesthroughthem. The leatherback is certainly not the only animal with such an arrangement; gulls have acountercurrentexchangein their legs. That is why agullcan stand on an ice floe without freezing.

All this applies, ofcourse, only to an adult leatherback. Hatchlings aresimplytoo small toconservebody heat,evenwithinsulationandcountercurrentexchangesystems. We do not know how old, or how large, a leatherback has to be before it canswitchfrom a cold-blooded to a warm-bloodedmodeof life. Leatherbacksreachtheirimmensesize in a much shorter time than it takes other sea turtles to grow. Perhaps theirrushto adulthood is driven by a simple need to keep warm.

Questions:
question_stem: The phrase “unique among” in the passage is closest in meaning to
choices: tag: A
text: natural to

tag: B
text: different from all other

tag: C
text: quite common among

tag: D
text: familiar to
answer_key: B
explanation: unique 独特，那么 unique among 就是在一大堆东西之间很独特的意思，所以答案是 B。本句说 leatherback turtle 比其他的乌龟能够向南或者向北游的更远，它们有一套什么样的应付冷水的方法。C 和 D 正好跟原文相反，如果都一样为什么还单独说这种 turtle 呢？而且这两个选项意思接近，都不选；至于 natural 是完全不靠谱的。

question_stem: What can be inferred about whales from paragraph 1?
choices: tag: A
text: They are considered by some to be reptiles.

tag: B
text: Their bodies are built in a way that helps them manage extremely cold temperatures.

tag: C
text: They are distantly related to leatherback turtles.

tag: D
text: They can swim farther than leatherback turtles.
answer_key: B
explanation: 选项 B 是对第一段的整体概括说明。
选项 A：鲸是爬行动物，原文并未提及 whale 是什么，错误。
选项 C：原文说他们 physiology 上像，没说它们是否相关，错误。
选项 D：原文并未提及此信息。

question_stem: The word “feat” in the passage is closest in meaning to
choices: tag: A
text: remarkable achievement

tag: B
text: common transformation

tag: C
text: daily activity

tag: D
text: complex solution
answer_key: A
explanation: A, feat: 功绩，成就。A 是卓越的成就；B 是一般的转化；C 是日常活动；D 是发杂的解决方案。所以答案 A 正确。

question_stem: Paragraph 2 mentions all of the following as true about the body heat of adult leatherback turtles EXCEPT:
choices: tag: A
text: Their muscles produce heat for maintaining body temperature.

tag: B
text: Their dark bodies help trap solar radiation.

tag: C
text: Their cellular metabolism produces heat as a by-product.

tag: D
text: Basking at the water’s surface helps them obtain heat.
answer_key: C
explanation: C 的 muscles 做关键词定位至最后一句，说可以通过肌肉的活动获得热量，正确，不选；B 的 dark body 做关键词定位至第三句，说黑色体表可以捕获太阳辐射，正确，不选；C 的 by-product 做关键词定位至第四句，但原文说不像我们和鸟类那样把热量作为新陈代谢的副产品，所以与 C 说的刚好相反，C 是答案；D 的 basking 和 surface 做关键词定位至倒数第二句，说通过 basking 可以获得热量，正确，不选。

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

tag: B
text: effort

tag: C
text: activity

tag: D
text: mass
answer_key: D
explanation: D bulk: 体积，容量，大块。A 是力量；B 是努力；C 是活动；D 是大量，块。所以答案是 D 的 mass。

question_stem: The word “it” in paragraph 4 refers to
choices: tag: A
text: the problem

tag: B
text: blood

tag: C
text: the turtle

tag: D
text: body temperature
answer_key: B
explanation: B 往前找，找 as 那句话的主语，发现主语是 blood，答案是 B，带进去说 blood 丧失热量说得通。A 和 D 带进去说不通，turtle 虽然在前文出现但都不是所在词组的核心名词，所以不选。

question_stem: According to paragraph 4, which of the following features enables the leatherback turtle to stay warm?
choices: tag: A
text: An insulating layer of blubber

tag: B
text: A thick, oily skin covering fatty tissue

tag: C
text: The aerodynamic shape of its flippers

tag: D
text: A well-insulated head
answer_key: B
explanation: 关键词不好找，可以用排除法。A 的 blubber 做关键词定位至第五段第一句的前半句，原文明显说没有，所以 A 说反；B 的 fatty tissue 做关键词定位至第五段第一句的后半句，原词重现，所以这个答案正确；C 的 flipper 做关键词定位至倒数第三和第四句，没说 flipper 和维持体温的关系，不选；D 的 head 做关键词定位至第五段第二句，同样没说 head 和维持体温的关系，不选。

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 or leave out essential information.
choices: tag: A
text: In a turtle's countercurrent exchange system, outgoing vessels lie near enough to ingoing ones that heat can be exchanged from the former to the latter before reaching the turtle's flippers.

tag: B
text: Within the turtle's flippers, there is a countercurrent exchange system that allows colder blood vessels to absorb heat from nearby warmer blood vessels and then return warmed blood to the turtle's body.

tag: C
text: In a countercurrent exchange system, a turtle can pick up body heat from being close enough to other turtles, thus raising its blood temperature as it passes them.

tag: D
text: When a turtle places its flippers close to its body, it is able to use its countercurrent exchange system to transfer heat from the warmer blood vessels in its body to the cooler blood vessels in its flippers.
answer_key: A
explanation: A 原句的结构是一个血管离另一个血管近，因此之间可以转移能量，所以答案 A 正确。B 的 within 那个状语原文就没说；原文说是一个血管离另一个血管近，不是一只乌龟靠近另一只乌龟，C 完全不靠谱；原文说两个血管靠的近，不是 D 说的冷血的血管在 flipper 里面；几个错误答案都偷换了原文的概念。

question_stem: Why does the author mention old-fashioned steam radiator in the discussion of countercurrent exchange systems?
choices: tag: A
text: To argue that a turtle's central heating system is not as highly evolved as that of other warm-blooded animals

tag: B
text: To provide a useful comparison with which to illustrate how a countercurrent exchange system works

tag: C
text: To suggest that steam radiators were modeled after the sophisticated heating system of turtles

tag: D
text: To establish the importance of the movement of water in countercurrent exchange systems
answer_key: B
explanation: 功能目的题，修辞点所在的句子只是单纯的说一个例子，而且开头就说 this the same，证明前句有答案。前句就是我们上题分析的句子，介绍了 countercurrent exchange system 是怎么运作的，所以答案是 B，将两者进行一个对比来展示这个系统的运作方式。A 的 argue 作者在原文没说，错；C 说 steam radiator 是跟乌龟学的，原文没有相关信息，错；D 的 water 只是单纯陈述的例子的一部分，不是观点，错。

question_stem: The phrase “courses through” in the passage is closest in meaning to
choices: tag: A
text: rises through

tag: B
text: heats up in

tag: C
text: runs through

tag: D
text: collects in
answer_key: C
explanation: C course:课程，轨迹，所以 course through 取轨迹的意思，“通过”之意，所以答案是 C。A 是升起；B 是加热，升温；D 是收集，收藏。

question_stem: According to paragraph 6, which of the following statements is most accurate about young leatherback turtles?
choices: tag: A
text: They lack the countercurrent exchange systems that develop in adulthood.

tag: B
text: Their rate of growth is slower than that of other sea turtles.

tag: C
text: They lose heat easily even with insulation and countercurrent exchange systems.

tag: D
text: They switch between cold-blooded and warm-blooded modes throughout their hatchling stage.
answer_key: C
explanation: 以 young leatherback turtle 做关键词定位至第二句，注意第二句中的 hatchling 与关键词同义重合。说幼崽因为身形太小，尽管有 countercurrent system 也不能保住身体的热量，所以答案是 C。A 说没有热交换系统与原文相反；B 选项与原文倒数第二句相反；D 冷热血变换原文没说。