Many aspects of the history of flowering plants (angiosperms) remainmysterious. Evidence of the earliest angiosperms comes from fossilized leaves, stems, fruits,pollen, and, veryrarely, flowers. In addition, there has been much study of modern plantmorphology(structure) andgeneticsin order todeterminewhich living species might be most closely related to the ancient ancestors of angiosperms. Despite intensive efforts for over 200 years, scientists have stillnot reachedconsensusonwhich type of plant was theancestorto the angiosperms, and when and where the angiosperms first evolved. Indeed, Charles Darwin himself called the origin of the flowering plants an “abominablemystery.”

What type of plant was theancestorto the angiosperms? Most botanists now agree that the flowering plants aremonophyleticin origin, meaning that they evolved from a commonancestor. Some paleontologists have suggested that the commonancestormay have been a type of cycad (palmliketropicalplants). Other paleontologists maintain that the angiosperms may have evolved from seed-bearing ferns. Finally,analysisof themorphologicaltraits of someprimitiveliving plants suggests that theancestormay have been related to the modern pines. The question ofangiospermancestry remains unresolved.

The time and place of the firstappearanceof flowering plants have long been a topic of great interest. There is goodfossilevidence that early angiosperms, including a number resembling modern magnolias, were present in the EarlyCretaceousgeologic period (more than 100 million years ago). Angiosperms became increasinglyabundantduring this period. Between 100 million and 65 million years ago, a period known as the LateCretaceous, angiosperms increased from less than 1 percent offlora(plant life) to well over 50 percent. Many of the modern plant families appeared during this time period. In the EarlyTertiaryperiod which followed, angiosperms increased tocomprise90 percent or more of Earth’s totalflora. Where did these successful plants firstoriginateandspreadfrom?

Analysisof thefossilleaf structure and geographicdistributionof the earliestCretaceousangiosperms has led many biogeographers to conclude that they evolved in the tropics and then migrated poleward. It is known that angiosperms did not becomedominantin the high latitudes until the LateCretaceous. Paleontologists have recoveredfossilangiospermleaves, stems, andpollenfrom EarlyCretaceousdeposits in eastern South America and western Africa. These two continents were joined together as part ofGondwanaland, one of two supercontinents that existed at that time. The locations of these earlyangiospermfinds would have been close to theequatorduring the EarlyCretaceousand are conformable with a model by which angiospermsspreadfrom the tropics poleward.

Not all botanists agree with an African-South American center for the evolution anddispersalof the angiosperms, pointing out that many of the mostprimitiveforms of flowering plants are found in the South Pacific, including portions of Fiji, New Caledonia, NewGuinea, eastern Australia, and the MalayArchipelago. Recentgeneticresearch has identified theraretropicalshrubAmborella as being the living plant most closely related to the ancientancestorof all the angiosperms. This smallshrub, which has tiny yellow-white flowers and red fruit, is found only on New Caledonia, a group of islands in the South Pacific. Many botanists conclude that the best explanation for the large numbers ofprimitiveliving angiosperms in the South Pacific region is that this is where the flowering plants first evolved and these modern species are relics of this early evolution. Comparisons of the DNA of Amborella and many hundreds of species of flowering plants suggest that the firstangiospermarose and the development of separate species occurred about 135 million years ago.

Recently discovered fossils complicate our understanding of the origin of the angiosperms even further. Paleontologists from China have found beautifully preserved fossils of anangiospermplant, including flowers and seeds, inJurassicperiod deposits from China. The site, which is about 130 million years old, is near modern Beijing. The newfossilplant found at the site is one of the oldest known angiosperms. The age of the fossils and the veryprimitivefeatures of the flowers have led the discoverers to suggest that the earliest flowering plants may have evolved in northern Asia.

Questions:
question_stem: The phrase “not reached consensus on” in the passage is closest in meaning to
choices: tag: A
text: not formulated a theory about

tag: B
text: not agreed on

tag: C
text: not been able to explain

tag: D
text: not found evidence for
answer_key: B
explanation: consensus 共识，not reached consensus on=not agreed on，无法达成共识。

question_stem: According to paragraph 1, all of the following types of evidence have been important for studying the history of angiosperms EXCEPT:
choices: tag: A
text: fossils of angiosperm stems and leaves

tag: B
text: knowledge of the structure of modern angiosperms

tag: C
text: large collections of well-preserved angiosperm flowers

tag: D
text: genetic studies of modern angiosperms
answer_key: C
explanation: 根据文段第2和3句，可对应 ABD 选项，C 选项的 large collections of…flowers 跟第2句中的 rarely， flowers（证据很少会来自花）相反，该选项错误，所以选 C。

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

tag: B
text: assume

tag: C
text: suspect

tag: D
text: claim
answer_key: D
explanation: maintain=claim，认为。

question_stem: According to paragraph 2, most botanists now believe which of the following about angiosperms?
choices: tag: A
text: The ancestor of today’s angiosperms was most likely a palmlike tropical plant.

tag: B
text: Today’s angiosperms can be traced back to a single ancestor.

tag: C
text: Angiosperms likely evolved from three very different plants.

tag: D
text: Angiosperms share a common ancestor with modern pines.
answer_key: B
explanation: 题目问 most botanists 的看法，对应文段第2句话，来自一个共有的祖先，跟 B 选项对应， a common ancestor= a single ancestor。

question_stem: Which of the following can be inferred from paragraph 3 about angiosperms during the Early Cretaceous?
choices: tag: A
text: They represented less than 1 percent of plant life.

tag: B
text: Their numbers remained stable during this period.

tag: C
text: They existed in forms that are very unlike plants living today.

tag: D
text: They only rarely left traces in the fossil record.
answer_key: A
explanation: 题目问白垩纪早期的 angiosperms 能推出什么。根据该段落2-4句话，可知，angiosperms 在白垩纪早期就出现了，而且在这个时期持续增长，在白垩纪晚期的时候，该植物从不到1%的占比增长的超过50%，说明在白垩纪早期，这个物种的占比不到1%，选 A。B 选项的 stable 错误，这个时期是增长状态；C 中的 unlike 错，跟第2句话中的 resembling modern magnolias 冲突；D 选项说很少留下化石记录跟段落第2句话 there is good fossil evidence 冲突。

question_stem: Why does the author include the information that “fossil angiosperm leaves, stems, and pollen” have been found in places that were once joined together as part of Gondwanaland?
choices: tag: A
text: To provide support for the claim that angiosperms first appeared in the tropics

tag: B
text: To explain how scientists have determined the geographical location of supercontinents during Earth’s early history

tag: C
text: To provide evidence that angiosperms evolved in similar ways in different parts of the world

tag: D
text: To challenge the idea that angiosperms spread toward the poles during the Cretaceous
answer_key: A
explanation: 该题型重点找题干细节所要论证的观点句，对应文段第1句话中 conclude that 后面的观点，说明 angiosperms 是在热带进化再迁移到极地的，对应 A 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 leaveout essential information.
choices: tag: A
text: Some botanists who agree with the idea of an African-South American center for the dispersal of angiosperms point to primitive South Pacific angiosperms as evidence.

tag: B
text: Some botanists argue that the very primitive forms of angiosperms found in the South Pacific call into question the theory that angiosperm evolution began in Africa and South America.

tag: C
text: Angiosperms in Fiji, New Caledonia, New Guinea, eastern Australia, and the Malay Archipelago are more primitive than angiosperms in other parts of the world.

tag: D
text: Botanists disagree over whether the most primitive forms of living plants are located in parts of Africa and South America or in the South Pacific.
answer_key: B
explanation: 该句核心意思是：不是所有的植物学家都赞同非洲和南美洲是 angiosperms 进化和扩散的中心，他们指出很多原始的开花植物在南太平洋被发现。
A 选项中 who agree with the idea…错误，他们是不赞同；
B 选项“一些植物学家认为在南太平洋找到的原始 angiosperms，质疑了 angiosperms 在非洲和南美洲进化这个理论”该选项符合原句子意思，正确；
C 选项中的 more primitive 这个比较级原文没有提到；
D 选项没有把原句子的重点--不赞同非洲北美理论--传达出来，该选项排除。

question_stem: According to paragraph 6, which of the following is true of angiosperm fossils discovered in China?
choices: tag: A
text: They have made it even more challenging to understand the origin of angiosperms.

tag: B
text: They contain flowers that appear modern for the age of the fossils.

tag: C
text: They convinced most botanists that angiosperms did not originate in northern Asia.

tag: D
text: They are not as old as angiosperm fossils discovered in the South Pacific.
answer_key: A
explanation: 结合文段第一句话，中国发现的证据让我们对 angiosperms 的来源的理解变得更复杂了，对应 A 选项。B 选项未提及；C 选项跟最后一句话冲突；D 选项错误，根据倒数第2句话，中国的发现目前是最早的，跟 D 选项的 not as old as…相反，排除。