There are many interesting adaptations that allow plants tosurvivein cool environments. Oneobviousstrategyisdormancy(asuspensionofactivity) during the coldseason. Most of thecommontrees in the forests of northeastern North America, western Europe, and eastern Asia, such as the maples, oaks,beech, birches, and ashes, aredeciduoustrees that lose their frost-sensitive leaves during the cold winterseason. In most of these trees, the leaves suffer damage at temperatures of freezing or just below. The new leaves arise in thespringfrom winter buds that canremainviableat colder temperatures.

Most of the needle-leaved conifers of the northern andalpineforests, such as pines, spruces, and firs, do not lose their leaves during the winter. How do suchevergreenplantsescapeintracellular freezing (freezingwithincells) andtissuedestructionwhen temperatures maydropto -40℃ or colder? In these plants, the onset of cool temperatures causesphysiologicalchanges that allow planttissueto eitheravoidfreezing orrestrictfreezing to extracellular areas (those outside of cells). For plants toavoidfreezing, they must chemicallyaltertheir liquids into a form that isanalogousto antifreeze in automobiles. The liquids in these plants can be cooled far below 0℃ and will notfreeze. Thisprocessis called supercooling and is achieved by themetabolicsynthesisof sugars and other molecules which, when insolutionin the plant'stissue,lowerthetemperaturefor iceformationto far below 0℃. Supercooling seems to be theprevalentmechanismoffrostresistancein herbs. For woody plants, supercooling is augmented by declines of cellular watercontent, greater cellularaccommodationto deformation, and processes that allow water toaccumulateandfreezein extracellular spaces. The loss of water from the cells to extracellular areas increases the solutecontent(thequantityof dissolved substances) of theremainingcellwater, making it moreresistantto freezing. Thecellwalls canaccommodatethe deformations caused by water freezing on theexteriorof thecell. For northern andalpineevergreens such as pines and spruces, both supercooling and extracellular iceformationplay a part in allowing the plants towithstandextremely cold temperatures. One interestingfacetof thesephysiologicaladaptations to freezing is that most of these plants will still be damaged by cold temperatures if they do not have a period of cooling in which toadjustto the onset of winter. Thisprocessofphysiologicalpreparation for the onset of winter cold is calledfrosthardening.

Some members of thecactusfamilyappeartoresistfreezing during cool nights by radiating heat stored during the day in their thick,moisttissue. The greater themassof thecactus, the more heat it can store and the lessproneit will be to freezing damage during the night. How is it then that these cacti cansurvivecold temperatures when they are young and small? Thegiantsaguarocactusis perhaps the best-knownsymbolof the southwesterndesertof North America. In thepopularloreof North America, thedistinctiveshapeof the multistemmed saguaro is a universally recognized icon that is used torepresentdeserts in movies, television, and comics. Yet, thisdistinctiveand widely recognized plant is actually found only in the SonoranDesertof California, Arizona, andadjacentMexico. The saguarocactusis damaged or killed ifexposedtoprolongedfreezing temperatures. Desertclimates in the northern SonoranDesertare typified by warm days but sometimes experience nighttime temperatures that are below freezing in the winter. Young saguaros thatsurviveare foundshelteredbeneathmore frost-tolerantdesertshrubs. The cover of these shrubs acts as athermalblanket, capturing heat radiated from the ground and keeping the microclimate of the small saguaro warm at night. As thecactusgrows, iteventuallyrises above the cover of the protectiveshrub. Theradiationof heat from thestalkof the largematurecactusprevents freezing. Thisstrategyworks up to a point. The range of the saguaro isrestrictedto areas that do not experience more than about 12 to 24continuoushours ofairtemperatures below 0℃. It appears that after 24 hours of freezingairtemperatures, not enough heatreserveis left in the saguaro to keep thetissuefrom freezing.

Questions:
question_stem: According to paragraph 1, which of the following is true of trees like maples and oaks?
choices: tag: A
text: They have leaves that are resistant to frost.

tag: B
text: They are unable to survive if their leaves are damaged.

tag: C
text: They have buds that do not produce new leaves until temperatures rise.

tag: D
text: They can delay the production of buds until the arrival of spring.
answer_key: C
explanation: 题干提问“以下哪个有关枫树和橡树的描述是正确的”。
定位第1段最后一句 The new leaves arise in the spring from winter buds that can remain viable at colder temperatures.（春季，新叶从冬芽中长出，在较冷的温度下仍能存活。）可理解为春天就会发芽生叶了，对应选项 C 表述。
选项 A 与第4句 deciduous trees that lose their frost-sensitive leaves during the cold winter season 说反，落叶树冬季需要掉叶；选项 B 与原文不符，只是冬季掉叶并不是不能存活；选项 D 与原文不符，winter buds 即在冬天就有 buds，并没有 delay bud production。
故选 C。

question_stem: Why does the author ask the question, "How do such evergreen plants escape intracellular freezing (freezing within cells) and tissue destruction when temperatures may drop to -40℃ or colder?" in the passage?
choices: tag: A
text: To introduce an account of the ways evergreen plants protect themselves from the cold

tag: B
text: To suggest that losing their leaves would allow evergreens to escape damage from the cold

tag: C
text: To point out that scientists do not fully understand how evergreens survive cold temperatures

tag: D
text: To emphasize that studying evergreens may hold the key to understanding how all forest plants survive cold temperatures
answer_key: A
explanation: 题干提问“作者为什么要提这个问题？”。
定位第2段第2句高亮句，是一个设问句，设问句的功能就是引出下文，下文应是对该设问句的回答，对应选项 A 表述。
故选 A。

question_stem: The author mentions "antifreeze in automobiles" in the passage in order to
choices: tag: A
text: emphasize the difficulty trees such as conifers have in surviving

tag: B
text: point out that freezing temperatures can seriously damage tree tissue

tag: C
text: illustrate a chemical process in plants that prevents them from freezing

tag: D
text: explain how conifers are able to raise the temperature in their tissue
answer_key: C
explanation: 题干提问“作者提及‘汽车防冻剂’是为了”。
定位第2段第4句 For plants to avoid freezing, they must chemically alter their liquids into a form that is analogous to antifreeze in automobiles. （为了避免结冰，植物必须用化学方法将液体转变成一种类似汽车防冻剂的形式。）根据 analogous to 表达出的类比关系，可理解为利用 antifreeze in automobiles 类比说明植物防冻时的化学变化，对应选项 C 表述。
故选 C。

question_stem: According to paragraph 3, why does the mass of a cactus influence its ability to resist freezing?
choices: tag: A
text: Larger cacti tend to have less water in them, making freezing less likely.

tag: B
text: Larger cacti can store more heat in their tissues and thus stay warmer at night.

tag: C
text: Cacti with more mass tend to have deeper roots that take longer to freeze.

tag: D
text: Cacti with more mass exchange more moisture with the air, which protects them from the cold.
answer_key: B
explanation: 题干提问“为什么仙人掌的质量会影响它抵抗冰冻的能力”。
定位第3段第2句 The greater the mass of the cactus, the more heat it can store and the less prone it will be to freezing damage during the night.（仙人掌的质量越大，它能储存的热量就越多，在夜间受到冻伤的几率就越小。）对应选项 B 表述。
故选 B。

question_stem: The word "prolonged" in the passage is closest in meaning to
choices: tag: A
text: unexpected

tag: B
text: extreme

tag: C
text: frequent

tag: D
text: extended
answer_key: D
explanation: prolonged adj.持久的，长期的，与 extended 同义。
故选 D。

question_stem: Paragraph 3 supports which of the following claims about the ability of saguaro cacti to survive freezing temperatures?
choices: tag: A
text: Saguaro cacti,whether large or small, have no resistance to freezing because they seldom face freezing temperatures.

tag: B
text: Saguaro cacti living in the Sonoran Desert are less likely to die from freezing than those living in other areas of the North American southwest.

tag: C
text: In different ways, both young and mature saguaro cacti are protected during a freezing night by heat that had been stored during the day.

tag: D
text: Mature saguaro cacti can survive in areas that are too cold for the frost tolerant shrubs that shelter young saguaro cacti.
answer_key: C
explanation: 题干提问“以下哪个描述符合仙人掌在冰点可以存活的能力”。
定位第3段第9-12句 Young saguaros that survive are found sheltered beneath more frost-tolerant desert shrubs. The cover of these shrubs acts as a thermal blanket, capturing heat radiated from the ground and keeping the microclimate of the small saguaro warm at night. As the cactus grows, it eventually rises above the cover of the protective shrub. The radiation of heat from the stalk of the large mature cactus prevents freezing. 即沙漠灌木丛给小仙人掌提供温暖，大仙人掌靠自己提供温暖，对应选项 C 表述。
故选 C。

question_stem: It can be inferred from paragraph 3 that saguaros are limited to areas in which
choices: tag: A
text: young cacti can grow taller than the shrubs surrounding them

tag: B
text: temperatures remain below freezing for periods that do not exceed 24 hours

tag: C
text: daytime temperatures are sufficiently high to enable cacti to store a lot of heat

tag: D
text: there is enough heat radiated from the ground to protect cacti from freezing air temperatures
answer_key: B
explanation: 题干提问“仙人掌被限制在什么范围”。
定位第3段最后2句 The range of the saguaro is restricted to areas that do not experience more than about 12 to 24 continuous hours of air temperatures below 0℃. It appears that after 24 hours of freezing air temperatures, not enough heat reserve is left in the saguaro to keep the tissue from freezing.即冰冻温度不能超过24小时，对应选项 B 表述。
故选 B。

question_stem: All of the following questions are answered in the passage EXCEPT:
choices: tag: A
text: How does supercooling work to prevent liquids in plants from freezing?

tag: B
text: Why does the loss of water from plant cells and the collection of water in extracellular areas protect the water inside the cells from freezing?

tag: C
text: How do members of the cactus family limit heat radiation during daylight hours?

tag: D
text: How do frost -tolerant shrubs help protect young saguaro cacti from being damaged by extreme nighttime winter temperatures?
answer_key: C
explanation: 题干提问“根据全文，以下哪个问题没有被解答”，建议先看完四个选项，再逐一对应文本。
选项 A 对应第2段 This process is called supercooling and is achieved by the metabolic synthesis of sugars and other molecules which, when in solution in the plant's tissue, lower the temperature for ice formation to far below 0℃.，被解答，正确；
选项 B 对应第2段 The loss of water from the cells to extracellular areas increases the solute content (the quantity of dissolved substances) of the remaining cell water, making it more resistant to freezing.，被解答，正确；
选项 C 对应第3段，未讨论 limit heat radiation during daylight hours，没有被解答，错误；
选项 D 对应第3段 The cover of these shrubs acts as a thermal blanket, capturing heat radiated from the ground and keeping the microclimate of the small saguaro warm at night. ，被解答，正确。
故选 C。