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2019年10月26日托福閱讀機經部分內容供大家參考，機經雖然只是作為參考的題庫，但是托福考試重復歷年真題也是大大存在的，尤其是近三年的考題。
話題一：生物
生物類話題占據托福考試的30%左右，出現頻率一直處于首位。生物類話題主要包括動、植物介紹，以及生物常識。動物常考的有昆蟲、魚、蜜蜂、有袋動物、恐龍、鳥類;植物常考的有海草、沙漠植物、松樹、花粉、草原;生物常識包括基因隔離、生物遷徙、休眠、達爾文進化論、轉基因植物。
可再考真題
①2016-7-10CN 熱帶雨林的動物
熱帶雨林物種多樣性，熱帶雨林物種多，那里的植被超過1000種，歐洲有40種(此處考題：為什么作者提到歐洲有40種物種)。熱帶雨林為什么物種多呢?大平原的動物要走很久才能尋找到合適的生活地點。熱帶雨林的動物不能，他們被限制在小空間內。(此處記憶模糊)熱帶云林里的屏障阻礙動物們spread。如何阻礙。幾十到50米有天河the upsets(好像是這個詞來著)canopy,是熱帶樹種濃密的樹葉和枝干各種交織形成的，動物們很難突破這層canopy,只能在舉例近的canopy之下活動，所以無法spread到外界。(考題：為什么動物不能spread出去?答案就是帶leaves和roots 的那個。)所以限制在內的描物們就diversify各種。50-70米是超級離的且喜陽光的樹種們為了曬太陽浴而拼命生長突破Z高 canopy形成的。因此有種S鳥躭生活在這里，他們可以去任何地方，所以列舉了三個州有這種鳥，而且種類較少(考題:問作者列舉S鳥目的是啥?為了說明有屏障species會分類于是種類變多)。他們俯瞰著森林抓里面的 monkey各種，如同south America (應該是這里)的體系(考題: S鳥的體系和SA哪相同?答案就是帶technique那個就是獵食體系都是站在上面俯瞰)。緊接著將Karol這種樹，因為突破canopy 長得高可以將種子敗播超級遠，于是South America哪都有(考題：問S鳥和K樹有啥區別?三洲都有)。
②2016-10-16CN 沙漠里的生命
本文共5段。第1段講了沙漠中環境惡劣，但仍有許多生物生存。Z大的問題是缺水，生物發展出了適應缺水環境的本領。第2段講到一年和多年生植物各自的適應方法。第3段講到沙漠中的惡劣環境還有缺食物。第4段講了動物適應沙漠環境所做的改變。第5段講到適應沙漠環境還可以在form和 function上改變。
③2016-9-24CN 有袋動物
本文共4段：第1段引出所有的哺乳動物都是placental (胎盤)動物，除了Opossum(負鼠，袋貂)。該段以opossum為例區分marsupial類動物與哺乳動物之間的差異和不同，講到了Opossum的形態特征，生理特征等;
第2段講到Opossum的進化歷史，從澳大利亞，南美洲，和非洲板塊還在一起是，opossum就已經存在，后來三塊大陸分開，opossum就被分割到三地。在澳大利亞的opossum進化成了袋鼠，考拉;
第3段講北美和南美洲連接在一起后，opossum的種群數量大量下降，但是沒有滅絕。而且根據化石記錄，它們沒有發生進化變成別的物種，而是保持了原來的狀態，也即使我們現在看到的袋貂。
第4段講到opossum曾經在北美洲的遷徙和現在分布狀態，主要分布與俄亥俄州，弗吉尼亞州和加拿大。
④2016-5-22CN 昆蟲翅膀的畫
第一段：引入話題，翅膀化石fossil，引發很多猜測speculation。
第二段：講了原始翅膀protowings，提出了一個theory，講了翅膀的作用。
第三段：說第一個理論存在問題，protowing需要和身體以某種方式連接hinged，而且需要有肌肉控制翅膀的拍動，所以提出了另外一個理論解釋翅膀的起源。其中很多專業名詞，但是題目特別簡單(問什么導致了insectZ終能飛行，定位在Z后一句話finally，larger muscle讓昆蟲飛起來) 。
第四段：支持第二個理論，反對第一種理論的證據是化學傳感器chemical-sensing organs不在背上，在legs上。 第二、三段中有EXCEPT題，問第一個理論的problems是什么，兩段的開頭句逐個對應即可。
第五段：提出第三個理論，protowings來自于水中的一種昆蟲insect的腮gill。問句：翅膀是怎么從水中到飛行的?答案是通過翅膀產生推動力浮在水面上，當muscle越來越強大，滑的越來越快，Z后一飛沖天[有事實信息題]。
第六段：講飛行的作用：雖然上面的理論還有爭議，但是wing的作用是傳播dispersal或avoid predator，尤其考慮到predators的數量，躲避predator才是Z重要的目的[有句子簡化題，注意轉折關系]。躲避predator的機制是一種預警機制warning system，通過sense wind or vibration[有事實信息題，定位后能看懂wind即可選出。
⑤2016-5-29CN 極溫條件下的生物
地球上的溫度很少超過50℃，生物在高溫以及低溫條件下都很難生存，由于生物體內的一些生理過程隨溫度的升高反應速度變快，酶的活性也受溫度影響。絕大部分生物在40℃的代謝速度大約是10℃時的2至4倍(不同物種之間會有差異)。高溫條件下，大部分生物都不能存活，除了生活在溫泉里的細菌，它們的生物分子之間如蛋白質分子之間結構會加強，來保證它們在高溫下不會depart，這種細菌能夠在80℃條件下生存，Z高能忍受110℃的環境。海水因為含鹽，冰點會低于零度，對魚很不利，因為這些魚的細胞對高鹽分很敏感，不能通過這種方式來防止freeze。這些魚細胞里的**會聚在一起，形成較高濃度來保證不結冰，冰雪在形成的時候，是在小的冰的晶核或者其他東西為晶核為基礎生長的。這種就是通過coating在細胞內起這種作用的晶核表面，來阻止結冰。極地地區一些陸生生物，也通過這種方式來抵御嚴寒的冬天。它們體內的**濃度在冬天Z高能達到30%。
⑥2016-6-25CN 生物休眠現象
生物存在的一種休眠現象，例子有袋鼠休眠體內受精卵什么的，來適應惡劣環境，環境好了停止休眠。
1. 很多生物都存在這么個period以適應環境。有些這種period可以非常長。
2. 可預期的惡劣環境比如季節性的變化呢， 生物當然就適應的比較好，有些不可預期的惡劣環境，生物也有自己的一套。
3. 袋鼠，大段都在講一種紅袋鼠怎么適應的。肚里懷了一個，兜里裝了一個，手里牽著一個，還時時刻刻想著要什么時候交配。
⑦2017-1-7CN Extinction of the Mammoths
第一段，介紹Mammoths(猛犸象)生活的時間，和滅絕的時間。猛犸象生活照距今180萬年到1.1萬年期間的更新世(Pleistocene)。在距今1.1萬年的時候，基本滅絕。滅絕原因是氣候變化。
第二段，氣候滅絕理論認為距今1.3萬年-1萬年的時候，氣溫上升了6℃，夏天變的更長更熱，冬天變得更長更冷。溫和氣候時間持續較短。這就影響了食草動物們的食物，也即是植被的生長。
第三段，該理論模型認為，如果猛犸象常常食用三種類型的食物A, B, C，氣候變化后，會使得這幾種植物生長地理位置發生變化，不再生長在同一處區域。猛犸象即使隨著水草遷徙。
第四段，因為猛犸象賴以生存的植被生長區的變化，導致猛犸象不再像以前一樣能獲得足夠的營養，導致猛犸象題型變小，數量減少。
第五段，同時，因為植被導致了猛犸象的遷徙，使得猛犸象的種群數量被隔離成很小的種群，不同種群之間無法繁殖。小種群內部的繁殖導致基因質量越來越差，Z終滅絕。
第六段，舉例證明，生活在歐亞大陸的猛犸象就符合上面給出的氣候滅絕理論模型。
第七段，對猛犸象食用的植物減少，營養降低導致猛犸象滅絕的理論的提出質疑。因為，雖然氣候變化，但北美地區的哥倫比亞猛犸象能夠很容易遷徙到附近160公里的水草豐美的地方，但是哥倫比亞猛犸象還是滅絕了。
第八段，對氣候變化導致滅絕提出質疑，提到猛犸象生活的更新世Pleistocene，至少有個22詞較大的氣候周期變化，之前的氣候變化都沒有導致猛犸象滅絕，這一次滅絕了，理論站不住腳。
⑧2017-2-18CN A revolution of grassland and herbivores
第1段講到草比起其它植物的優勢之處是它成功的防御機制。草被切割時，損失的是它生命生長中Z不重要的一部分，而把Zbasal 的部分保留了下來。第2段講到傳統觀點認為是氣候變化造成了了草場的進化。草場生長于在prairie and savanna分布的更加廣泛， 而在canopy forest較為少見。后者的生長環境更為濕潤。以前認為氣候變化造成草場進化,進而造成食草動物的進化。第3段反對理論指出可能是食草動物的進化造成了草場。比如新西蘭某地氣候適宜草場發展，可是,是在人類引入了食草動物之后草場才廣泛發展的;第4段說有可能是食草動物的進化導致了那些草場的發展，因為其它的植物并不具備足夠的防御機制來滿足它們的需求。
真題測練
①2014-5-17CN Habitat Selection(棲息地選擇)
Researchers who study habitat selection have proposed various models for the process. Marine biologist Peter F. Sale hypothesized the existence of a simple mechanism of habitat selection in fish that is based on levels of exploratory behavior. Sense organs monitor specific stimuli in the environment and send a summation of pertinent stimuli back to central-nervous-system centers, which regulate the amount of exploration. As the constellation of cues approaches some optimum level, exploratory behavior ceases and the animal stays where it is.
An alternative hypothesis is that an animal has a cognitive map of the ideal habitat and that its behavior is goal directed. However, working with a species of surgeonfish, Sale tested juveniles in laboratory tanks with various water depths and bottom covers under which fish could hide. Exploration time was least in the tank with shallow water and bottom covers and highest in the tank with shallow water and no bottom cover. In choice tests and field observations, most fish preferred shallow areas with bottom cover. Thus, Sale concluded, there is no need to suggest the inheritance of complex cognitive maps and goal-directed behaviors, rather, the animal simply moves around more in an unsuitable habitat and less in a suitable one.
Sale’s model still does not explain how the animal “knows” what is suitable and what is not, or how stimuli from multiple cues are integrated. Nor does it explain the role of photoperiod (the duration of the animal’s daily exposure to sunlight) in the response of dark-eyed juncos to photographs of their natural habitat. These wild-caught birds were presented a choice of viewing one of two 35-millimeter color slides showing different habitats. Birds kept in the lab under a winter photoperiod of nine hours of light and fifteen hours of darkness preferred (spent more time in front of) slides of their southern winter habitat. After day length was increased to fifteen hours of light and nine hours of darkness, the birds’ viewing preferences shifted to the northern summer habitat.
Social cues may also affect choice of habitat. Large juncos (usually males) dominate smaller individuals (usually females and juveniles) in wintering flocks. Biologist Ellen Ketterson explained the finding that females usually migrate farther south than males by hypothesizing that subordinate birds are forced to migrate farther to avoid competing with dominants. In their lab study, researchers E. Roberts and Peter Weigl found that during the short days (stimulating winter), small subordinate juncos showed the strongest preference for winter scenes.
Risk of predation and competition are other factors that may affect habitat use. Hairy-footed gerbils live in vegetated islands in a sea of sand in the Namib Desert of southern Africa. Habitat use was determined by tracks in the sand and by how quickly they gave up feeding at stations containing seeds mixed with sand. Gerbils preferred sites around bushes or grass clumps to open areas and were more active on new-Moon nights than on full-Moon nights. They also gave up feeding at seed trays sooner in open areas and on full-Moon nights. These differences were likely caused by greater risk of predation in open areas and when the Moon was full. When striped mice, a close competitor of the gerbil, were removed, gerbils increased foraging activity, especially in the grass clumps.
The immediate cues to which animals respond when selecting a habitat may not be the same as the ultimate factors that have brought about the evolution of the response. For example, the blue tit, a European bird, lives in oak woodlands where most of its preferred food is found. But the blue tit establishes its territory each year before leaves and caterpillars (its staple food) have even appeared, so it must be using some other cue, such as the shape of the trees, to select its habitat. In fact, we know little about the signals that animals respond to when choosing their habitat. And in migratory species, it is not even clear when in the life cycle a choice of habitat is made. One study found that breeding sites may be selected in late summer or fall before migration, rather than in the spring, as is usually assumed.
Paragraph 1
Researchers who study habitat selection have proposed various models for the process. Marine biologist Peter F. Sale hypothesized the existence of a simple mechanism of habitat selection in fish that is based on levels of exploratory behavior. Sense organs monitor specific stimuli in the environment and send a summation of pertinent stimuli back to central-nervous-system centers, which regulate the amount of exploration. As the constellation of cues approaches some optimum level, exploratory behavior ceases and the animal stays where it is.
1. The word “pertinent” in the passage is closet in meaning to
A. important
B. selected
C. strong
D. relevant
2. According to paragraph 1, all of the following are processes that occur during exploratory behavior EXCEPT:
A. A favorable combination of cues are gathered.
B. Sense organs detect and record stimuli in the surrounding area.
C. Sense organs receive further directions from the central nervous system.
D. The central nervous system receives a summary of stimuli from the sense organs.
3. The word “ceases” in the passage is closet in meaning to
A. stops
B. decreases
C. succeeds
D. occurs
Paragraph 2
An alternative hypothesis is that an animal has a cognitive map of the ideal habitat and that its behavior is goal directed. However, working with a species of surgeonfish, Sale tested juveniles in laboratory tanks with various water depths and bottom covers under which fish could hide. Exploration time was least in the tank with shallow water and bottom covers and highest in the tank with shallow water and no bottom cover. In choice tests and field observations, most fish preferred shallow areas with bottom cover. Thus, Sale concluded, there is no need to suggest the inheritance of complex cognitive maps and goal-directed behaviors, rather, the animal simply moves around more in an unsuitable habitat and less in a suitable one.
4. In paragraph 2, why does the author discuss Sale’s research with a species of surgeonfish?
A. To demonstrate how animals distinguish suitable habitats from unsuitable ones
B. To give an example of an animal that shows little or no exploratory behavior during habitat selection
C. To challenge the hypothesis that animals have complex cognitive maps of their ideal habitat that guides their habitat selection
D. To provide evidence that fish prefer areas that are shallow and have covering under which to hide.
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