Theevolutionaryhistoryof plants has beenmarkedby aseriesof adaptations. The ancestors of plants werephotosyntheticsingle-celled organisms probablysimilarto today'salgae. Like modernalgae, the organisms that gave rise to plantspresumablylacked true roots, stems, leaves, andcomplexreproductivestructures such as flowers. All of these features appeared later in theevolutionaryhistoryof plants. Of today’s different groups ofalgae, greenalgaeare probably the mostsimilarto ancestral plants. This supposition stems from the closephylogenetic(naturalevolutionary) relationship between the two groups. DNA comparisons have shown that greenalgaeare plants’ closest living relatives. Inaddition, other lines ofevidencesupport thehypothesisthat land plants evolved from ancestral greenalgaeused the same type ofchlorophyllandaccessorypigments inphotosynthesisas do land plants. This would not be true of red and brownalgae. Greenalgaestore food asstarch, as do land plants and havecellwalls made ofcellulose,similarincompositionto those of land plants. Again, the goodstorageandcellwall molecules of red and brownalgaeare different.

Today greenalgaelive mainly in freshwater, suggesting that their earlyevolutionaryhistorymay have occurred in freshwater habitats. If so, the greenalgaewould have been subjected toenvironmentalpressures that resulted in adaptations that enhanced theirpotentialto give rise to land-dwelling or organisms.

Theenvironmentalconditions of freshwater habitats, unlike those of ocean habitats, are highlyvariable.

Watertemperaturecanfluctuateseasonally orevendaily and changinglevelofrainfallcanleadto fluctuations in theconcentrationof chemical in

the water orevento period in which theaquatichabitatdries up. Ancientfresh water greenalgaemust have evolved features that enable them towithstandextremes oftemperatureand periods of dryness. These adaptations served theirdescendantwell as they invaded land.

Theterrestrialworld is green now, but it did not start out that way. When plants first made thetransitionashore more than 400 million years ago, the land wasbarrenanddesolate,inhospitableto life. From a plant’sevolutionaryview point, however, it was also a land ofopportunity, free of competitors and predators and full ofcarbondioxideand sunlight (therawmaterials forphotosynthesis, which are present in far higher concentrations inairthan in water). So once naturalselectionhad shaped the adaptations that helped plantsovercomethe obstacles toterrestrialliving, plants prospered and diversified.

When plants pioneered the land, they faced a range of challenges posed byterrestrialenvironments. On land, the supportive buoyancy of water is missing, the plant is no longer bathed in anutrientsolution, andairtends to dry things out. These conditionsfavoredtheevolutionof the structures that support the body, vessels thattransportwater and nutrients to all parts of plant, and structures thatconservewater. The resulting adaptations to dry land include somestructuralfeatures that arose early in plantevolution; now these features arecommontovirtuallyall land plant. They include roots orrootlike structures, awaxycuticle that covers the surfaces of leaves and stems and limits theevaporationof water, and pores called stomata in leaves and stems that allow gasexchangebut close when water isscarce, thus reducing water loss. Other adaptations occurred later in thetransitiontoterrestriallife and now widespreadbut not universal among plants. These include conducting vessels thattransportwater and minerals upward from the roots and that move thephotosyntheticproducts from the leavesto the rest of the plant body and the stiffeningsubstancelignin, which support the plant body, helping itexposemaximumsurface area to sunlight.

These adaptations allowed an increasingdiversityof plant forms toexploitdry land. Life on land, however, also required new methods of transportingspermto eggs. Unlikeaquaticandmarineforms, land plants cannot alwaysrelyon water currents to carry their sex cells anddispersetheirfertilizedeggs. So the most successful groups of land plants are those that evolved methods offertilizedsexcelldispersalthat areindependentof water and structures thatprotestdeveloping embryos from drying out. Protected embryos and waterlessdispersalof sex cells were achieved with theoriginof seed plants and the keyevolutionaryinnovations that they introduced:pollen, seeds, and later, flowers and fruits.

Questions:
question_stem: The word “presumably” in the passage is closest in meaning to
choices: tag: A
text: originally

tag: B
text: supposedly

tag: C
text: obviously

tag: D
text: usually
answer_key: B
explanation: presumably 大概，可能，所以正确答案是 B 的 supposedly。不认识的同学想想 assume，叫做假定或者推断，由于前缀 pre 只表方向或者加强，所以这个词大致意思和 assume 差不多，代入，植物的祖先是光合作用的单细胞生物，怎么样缺乏根茎等等，由于植物的祖先谁也不知道是啥样，所以单细胞生物形成的植物是没有根茎等等东西这个结论只是个推测，正确答案 B。

question_stem: According to paragraph 1, all of the following are true of ancestral plants EXCEPT
choices: tag: A
text: They had cellulose-based cell walls.

tag: B
text: They were closely related to green algae

tag: C
text: They were able to store nutrients

tag: D
text: They had a sophisticated multicellular structure.
answer_key: D
explanation: D 排除法，A 的 cellulose based cell walls 和 C 的 store nutrients 都可以定位至倒数第二句，两个选项都正确，不选； B 的 green D 的 multicellular structure 与原文第二句的信息相反，错，选；事实上，这道题根本不需要排除，因为 D 选项直接跟上题的信息相反.

question_stem: The phrase “subjected to” in the passage is closest in
choices: tag: A
text: restricted by

tag: B
text: distant from

tag: C
text: exposed to

tag: D
text: combined with
answer_key: C
explanation: C  been subjected to: 遭受，承受。A 选项是受限于，B 是远离于，C 是暴露于，使遭受；D 选项是与…结合。根据词意，C 为正确选项。

question_stem: What can be inferred from paragraph 3 about ancient green algae?
choices: tag: A
text: They lived in a generally wet environment that was sometimes dry

tag: B
text: They adapted better to changes in water temperature than did to other changes in the environment.

tag: C
text: They inhabited areas that were close to the ocean.

tag: D
text: They had lived primarily on land
answer_key: A
explanation: A  以 ancient green algae 做关键词定位至最后两句，说古代 algae 可以忍受极端温度和一段时间的干旱，正好就是 A 说的 sometimes dry，所以 A 是答案。B 比较了水温的变化和其他因素的变化，而原文没给出任何相关信息，错；C 的 close to the ocean 好像没有干旱的时候吧；D 的 on land 是不是太干了？

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

tag: B
text: hardened

tag: C
text: deserted

tag: D
text: dried out
answer_key: C
explanation: C desolate: 荒凉的。A 选项是落满灰尘的，B 选项是变硬的，C 选项是荒芜的，D 选项是干旱的。根据词意，C 是正确选项。

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: Terrestrial plants had the advantages of not having rivals and having easy access to photosynthetic material

tag: B
text: The abundance of photosynthetic material made life on land easier for pioneering plants

tag: C
text: Once plants had eliminated their competitors and their predators, their evolutionary process proceeded smoothly.

tag: D
text: Plant evolution eliminated competitors and made the process of photosynthesis more efficient.
answer_key: A
explanation: A 整句话的主干重点内容是：land of opportunity，并且这个后面的 free of competitors and predators and full of carbon dioxide and sunlight 是对这个特点的同位语，起到补充作用，等于 land of opportunity。A 选项涵盖了这个主要内容。B 选项遗漏了 free of competitors; C 选项 once 的这个逻辑关系错误，且和原句有较大出入; D 选项改动较大。

question_stem: According to paragraph 4, which of the following is true about the terrestrial world at the time it was colonized by plants?
choices: tag: A
text: it was exposed to high levels of solar radiation

tag: B
text: it contained a limited supply of carbon dioxide

tag: C
text: it had developed 400million years earlier

tag: D
text: it lacked the presence of any organisms
answer_key: D
explanation: D 以 terrestrial world 做关键词定位至首句，说尽管现在很 green，最初不是，刚好问的是以前什么样，所以往下看。下一句说当植物登上陆地时，陆地是荒芜和贫瘠的，于是正确答案是 D，没有 organism。但说实话，个人认为这个答案并不好，但最初说选的 A 也有问题，原文讲的 sunlight 不能直接被 solar radiation 同义替换，比较而言还是 D 好些，B 和 C 完全不对.

question_stem: According to paragraph 5, all of the following are problems that early terrestrial plants had to overcome Except
choices: tag: A
text: a tendency to become dry

tag: B
text: the inability to limit surface sunlight

tag: C
text: the absence of a structure to support the body of the plant

tag: D
text: the inability to transport water and minerals through the plant
answer_key: B
explanation: B A 的 become dry 定位至第二句的 air tends to dry things out， A 正确，不选； C 的 support the body 和 D 的 transport water and minerals 定位至第三句，两个答案都正确，不选； B 的 sunlight 在最后一句，但跟问题问的什么困难根本不是一回事儿，错.

question_stem: the word “posed” in the passage is closest in meaning to
choices: tag: A
text: shared

tag: B
text: presented

tag: C
text: strengthened

tag: D
text: concealed
answer_key: B
explanation: B  pose:提出，造成。A 是共享，B 是提出，出现，C 是加强，D 是隐藏。根据词意，B 是正确选项。

question_stem: What purpose does paragraph 5 serve in the larger discussion of the origins of terrestrial plants?
choices: tag: A
text: To emphasize how long it took for ancestral plants to adjust to life on land

tag: B
text: To disprove the argument that land plants adapted easily to their new terrestrial environment

tag: C
text: To explain how plant colonization changed the physical environment of the terrestrial world

tag: D
text: To describe how ancestral plants solved the problems they confirmed in colonizing
answer_key: D
explanation: D 段落作用题：直接概括段落大意。段落大意通常出现在段落首句，而这一段首句也很明显是主旨句。表达出的意思就是当植物开辟陆地时，会遇到很多环境上的挑战。而后文则是叙述这些具体的挑战是什么，并且描述出了这些植物是如何发展出一些 adaptation 来适应这些环境的。前一段的末尾也说了 adaptation 帮助植物克服困难，很明显这一段是顺着上一段，进行具体描述如何克服的。这就和 D 选项的内容吻合。

question_stem: According to Paragraph 6, The adaptation made by terrestrial plants had which of the following effect?’
choices: tag: A
text: Plants developed reproductive strategies usable in both land and water environment

tag: B
text: the plant diversity achieved in water environments diminished on land

tag: C
text: seed plants became the dominant species among plants

tag: D
text: a greater range of plants was able to develop
answer_key: D
explanation: 以 adaption 做关键词定位至首句，说 adaption 使得干燥陆地上的植物越来越多样化，正好是题目问的影响，所以正确答案是 D 的 a greater range，more were available。A 跟 B 的水环境原文没有有说；C 的 seed plants 原文也没说

question_stem: Which of the following best describes the author’s presentation of the information about land plants？
choices: tag: A
text: the author provided and overview of the evolutionary relationships between specific species of algae and land plants

tag: B
text: The author discusses the transformation plants underwent in the process of changing from an aquatic to a terrestrial environment

tag: C
text: the author establishes a pattern of similarity between major land and water pant groups

tag: D
text: The author resents evidence to support the hypothesis that plants first fully evolved in water before finding their way to land
answer_key: B
explanation: B 从全文结构来分析，文章手段说了植物进化是需要有很多 adaptation 的，后面就开始说一开始是生活在淡水里，然后再入侵陆地，但是遇到很多挑战，接着就进化了很多 adaptations 去克服这些问题，并且开始 diverse 起来。这就和 B 选项的内容吻合，描述了植物从水生到陆生的转变。