Section II Reading Comprehension
Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. Mark your answers on the ANSWER SHEET.
Text 4
How do you know what a dinosaur ate? Guts rot away after death, so the details of dinosaur digestion remain obscure. The best indicators are teeth. Sharp, pointed teeth probably ripped chunks of flesh off prey for swallowing whole. Robust grinding surfaces suggest lots of chewing was involved. Yet many dinosaurs belonging to a group called the theropods, which gave rise to birds, lost their teeth altogether and evolved beaks. This has made it hard to work out what they ate and how they digested it.
There is, however, a second clue. Lots of dinosaurs had stones, known as gastroliths, in their stomachs. These are assumed to have assisted with digestion, and thus have their own tales to tell. And modern birds and crocodilians (which are both, like dinosaurs, members of a larger evolutionary group called the archosaurs) often have gastroliths, too.
Takasaki Ryuji at Okayama University of Science, in Japan, decided to investigate. In a study published in Paleobiology, he and his colleagues examined the gastroliths of 46 modern archosaur species (42 birds and four crocodilians) and compared them with those from 16 species of dinosaur.
The birds included herbivores, omnivores and carnivores. The crocodilians were all carnivorous. The shapes of the stones varied. As might be expected, if an animal had a highly muscular stomach (ducks and geese), its gastroliths tended to have been worn into the sorts of rounded shapes displayed by beach pebbles. Weaker stomachs (seabirds and crocodiles) contained more angular stones.
Looking at the dinosaurs, Dr Takasaki and his colleagues found that ornithischians (think Triceratops), a group which their teeth suggest were herbivores, retained angular gastroliths. These creatures, this implies, relied mostly on their jaws to grind up their food, leaving their stomachs to apply merely the finishing touches.
Long-necked sauropods (think Diplodocus) also had angular gastroliths. That is more of a puzzle, for these animals had pencil-like teeth using which, it is assumed, they stripped the leaves off tree branches that less cervically elongated animals were unable to reach. The explanation, Dr Takasaki suspects, is that like those of modern ungulates, sauropods’ stomachs depended mainly on fermentation to break food down.
Stones in the guts of theropods tell yet another story. Tarbosaurus, a hypercarnivore similar to Tyrannosaurus, and similarly endowed with sharp, pointed teeth, had angular gastroliths. However, theropods with beaks (of which science recognises at least four groups) had rounded ones. Indeed, Dr Takasaki saw a clear relation between tooth loss and stone roundness, as the work of grinding up food was transferred from jaws to stomach.
That shift may have helped make possible the evolutionary success of birds. Teeth are heavy, as are the jaw muscles those teeth require to do their job. This puts a lot of weight near an animal’s front. Shifting the job of grinding, and the muscles and hard surfaces involved, to the stomach centralises an animal’s centre of gravity in a way that would make it easier for it to rise from the ground.
Curiously, it is clear from the fossil record that the very earliest birds of all did not have beaks. But the fact that so many of their theropod relatives did, and that birds themselves evolved them at least twice, suggests the transition was easy. It may thus be that part of the secret to taking successfully to the skies was, quite literally, having the stomach for it.
36. According to Paragraphs 1 and 2, gastroliths are considered a useful clue mainly because ____
[A] they are more commonly preserved in the fossil record than teeth are
[B] they reveal what type of prey a dinosaur hunted rather than how it digested food
[C] they offer an alternative source of dietary information for dinosaurs whose teeth no longer indicate how they processed food
[D] they are found exclusively in dinosaur species that retained their teeth
37. According to Paragraph 4, the shape of a modern archosaur's gastroliths is closely related to ____
[A] whether the animal is classified as a carnivore or a herbivore
[B] the overall size of the animal's body relative to other archosaurs
[C] the specific type of prey the animal typically consumes
[D] how much muscular force its stomach exerts on the stones it contains
38. What do the findings on ornithischians and sauropods in Paragraphs 5 and 6 have in common?
[A] both groups are believed to have relied primarily on their stomachs rather than their jaws to process food
[B] both groups retained angular gastroliths despite relying on different digestive mechanisms
[C] both groups have since been reclassified as members of the theropod group
[D] both groups' teeth provided identical clues about how they broke down their food
39. According to Paragraphs 7 and 8, the shift from angular to rounded gastroliths in beaked theropods may have contributed to ____
[A] a redistribution of body weight that made it easier for these animals to become airborne
[B] an increase in the overall size of the animal's stomach cavity
[C] a reduction in the total number of gastroliths these animals needed to swallow
[D] a strengthening of the jaw muscles used to capture prey
40. What does the author suggest about the evolution of beaks in birds, according to the last paragraph?
[A] the earliest birds already possessed beaks before other theropods evolved them
[B] beaks were an essential prerequisite for any theropod species to achieve flight
[C] the fact that it occurred independently more than once implies it was a relatively straightforward evolutionary change
[D] the transition required dinosaurs to first develop rounded gastroliths before beaks could evolve
附注：根据历年考研英语真题阅读题源外刊等，摘选最新文章，模拟仿真出题。
参考答案见以下。
Quick look: CDBAC
36.【正确答案】C
【解析】题型：举例目的题
定位：原文提到，许多兽脚类恐龙丢失了牙齿、演化出喙，这使得判断它们吃什么、如何消化变得困难；胃石则被视为"第二条线索"。
分析：胃石之所以被视为有用的线索，正是因为对那些牙齿已无法提供进食方式信息的恐龙（尤其是失去牙齿的兽脚类）而言，胃石提供了另一条了解其饮食的途径。选项C准确概括了这一作用。
干扰项：[A]"它们在化石记录中比牙齿更常见地被保存下来"——无中生有，原文未做这一保存概率的比较；[B]"它们揭示的是恐龙捕食何种猎物，而非如何消化食物"——事实相反，原文明确说胃石与"消化"相关，而非猎物类型；[D]"它们只出现在保留了牙齿的恐龙物种中"——事实相反，原文明确指出许多恐龙以及现代鸟类、鳄类都有胃石，并未局限于有牙齿的物种。
37.【正确答案】D
【解析】题型：细节理解题
定位：原文提到，胃部肌肉发达的动物（如鸭、鹅）体内的胃石往往被磨成海滩卵石般的圆润形状；胃部较弱的动物（如海鸟、鳄鱼）体内的胃石则更为棱角分明。
分析：胃石的形状与胃部对石头施加的肌肉力量密切相关——胃部肌肉越强，石头越容易被磨圆。选项D准确概括了这一关系。
干扰项：[A]"该动物被归类为食肉动物还是食草动物"——偷换概念，肉食性的鸟类和鳄类中都出现了胃石形状的差异，形状差异对应的是胃部肌肉强弱而非食性分类；[B]"该动物相对于其他初龙类的整体体型大小"——无中生有，原文未提及体型大小与胃石形状的关系；[C]"该动物通常捕食的具体猎物类型"——张冠李戴，原文强调的是胃部肌肉强弱这一生理因素，而非猎物类型。
38.【正确答案】B
【解析】题型：综合归纳题
定位：原文指出，鸟臀类（如三角龙）保留棱角状胃石，暗示它们主要依靠颌部研磨食物；蜥脚类（如梁龙）同样保留棱角状胃石，但推测其原因是它们的胃主要依靠发酵来分解食物，类似现代有蹄类动物。
分析：两个类群都保留了棱角分明的胃石，但背后的消化机制并不相同——一个依靠颌部研磨，一个依靠发酵作用。选项B准确概括了这一共同点与差异并存的关系。
干扰项：[A]"两个类群都被认为主要依靠胃部而非颌部来处理食物"——事实相反，鸟臀类恰恰是依靠颌部，蜥脚类依靠的是发酵而非胃部研磨；[C]"两个类群此后都被重新归类为兽脚类的成员"——无中生有，原文未提及任何重新分类；[D]"两个类群的牙齿提供了完全相同的食物分解线索"——以偏概全，蜥脚类"铅笔状"牙齿的线索与鸟臀类不同，二者牙齿提示的进食方式并不相同。
39.【正确答案】A
【解析】题型：推理判断题
定位：原文提到，牙齿及支撑其工作的颌部肌肉都很重，这会让动物的前部（头部）负重较大；将研磨食物的工作转移到胃部，能使动物的重心更居中，从而更容易离地升空。
分析：喙类兽脚类胃石从棱角状转变为圆润状，反映出研磨工作从颌部转移到了胃部，这种重量重新分布可能让这类动物更容易实现飞行离地。选项A准确概括了这一推论。
干扰项：[B]"该动物胃腔的整体大小有所增加"——无中生有，原文未提及胃腔大小的变化；[C]"这类动物需要吞下的胃石总数有所减少"——无中生有，原文未提及胃石数量的减少；[D]"用于捕食的颌部肌肉得到了强化"——张冠李戴，原文说的恰恰是颌部（及其肌肉）的负担被转移走了，而非被强化。
40.【正确答案】C
【解析】题型：主旨大意题
定位：末段提到，鸟类至少独立演化出喙两次，这一事实暗示这一转变"很容易"。
分析：喙这一特征在鸟类演化史上独立出现了不止一次，作者据此推断这种转变在演化上相对容易实现。选项C准确概括了这一推论。
干扰项：[A]"最早的鸟类在其他兽脚类演化出喙之前就已经拥有喙"——事实相反，原文明确说"最早的鸟类根本没有喙"；[B]"喙是任何兽脚类物种实现飞行的必要前提"——程度夸大，原文并未做出这种绝对化的必要条件判断，且提到最早的鸟类本身也没有喙；[D]"这一转变要求恐龙先演化出圆润的胃石，喙才能随后演化出来"——无中生有并因果颠倒，原文呈现的是"失去牙齿"与"胃石变圆"相关联，并非"胃石变圆"是喙演化的前提条件。
【词汇注释】
obscure: adjective (UNCLEAR) not discovered or known about; uncertain 模糊不清的；不为人知的
robust: adjective (STRONG) sturdy in construction; strong and healthy 坚固的；强健的（文中指研磨面坚固的牙齿）
gastrolith: noun (STOMACH STONE) a stone held in an animal's digestive tract to aid digestion 胃石
ungulate: noun (HOOFED ANIMAL) a hoofed mammal 有蹄类动物
fermentation: noun (CHEMICAL BREAKDOWN) the chemical breakdown of a substance by bacteria, yeasts or other microorganisms 发酵
centralise: verb (BRING TO CENTER) to bring something to a central point 使集中；使居中
endowed: adjective (POSSESSING) naturally having a particular ability, quality or characteristic 天生具有…的（文中指Tarbosaurus"天生具有"锋利的牙齿）
【长难句】But the fact that so many of their theropod relatives did, and that birds themselves evolved them at least twice, suggests the transition was easy.
主干为the fact...suggests the transition was easy（……这一事实表明这种转变是容易的）； the fact后接两个并列的that引导同位语从句：that so many of their theropod relatives did（它们众多的兽脚类近亲确实演化出了喙）和that birds themselves evolved them at least twice（鸟类自身也至少独立演化出喙两次），共同构成fact的具体内容。
【参考译文】
如何得知恐龙吃什么？恐龙死后内脏会腐烂，因此恐龙的消化过程细节仍然难以捉摸。最好的线索是牙齿。锋利的尖牙可能用来撕下猎物的肉块，以便整口吞下。坚硬的磨牙面表明它们需要大量的咀嚼。然而，许多属于兽脚类恐龙（鸟类的祖先）的恐龙完全失去了牙齿，进化出了喙。这使得我们很难弄清楚它们吃什么以及如何消化食物。
不过，还有第二个线索。许多恐龙的胃里都有被称为胃石的石头。人们认为这些胃石有助于消化，因此它们本身也蕴藏着许多故事。现代鸟类和鳄鱼（它们都和恐龙一样，属于一个更大的进化类群——主龙类）也常常拥有胃石。
日本冈山理科大学的高崎龙二决定对此展开研究。在《古生物学》杂志上发表的一项研究中，他和同事们检查了46种现代主龙类（42种鸟类和4种鳄鱼）的胃石，并将其与16种恐龙的胃石进行了比较。
这些鸟类包括草食性、杂食性和肉食性鸟类。鳄鱼均为肉食性鸟类。胃石的形状各不相同。正如预期的那样，如果一种动物的胃部肌肉发达（例如鸭子和鹅），其胃石往往会被磨成类似海滩鹅卵石的圆形。而胃部肌肉较弱的动物（例如海鸟和鳄鱼）的胃石则呈棱角分明的形状。
在研究恐龙时，高崎博士和他的同事发现，鸟臀目恐龙（例如三角龙）——尽管它们的牙齿表明它们是草食性动物——却保留了棱角分明的胃石。这表明，这些生物主要依靠颌部来磨碎食物，胃部只是起到最后的消化作用。
长颈蜥脚类恐龙（例如梁龙）的胃石呈角状。这更令人费解，因为这些动物拥有铅笔状的牙齿，人们推测它们用这些牙齿剥落颈部较短的动物无法触及的树枝上的树叶。高崎博士推测，其解释是，与现代有蹄类动物一样，蜥脚类恐龙的胃主要依靠发酵来分解食物。
兽脚类恐龙肠道中的结石则讲述了另一个故事。特暴龙是一种与霸王龙类似的超级食肉恐龙，同样拥有锋利的牙齿，其胃石呈角状。然而，长有喙的兽脚类恐龙（科学界至少将其分为四类）的胃石却是圆形的。事实上，高崎博士发现牙齿脱落与石头圆润度之间存在明显的关联，因为研磨食物的工作从颌部转移到了胃部。
这种转变或许促成了鸟类的进化成功。牙齿很重，咀嚼牙齿所需的颌部肌肉也很重。这使得动物的重心集中在身体前部。将研磨食物的工作以及相关的肌肉和坚硬的表面转移到胃部，可以使动物的重心集中，从而更容易从地面起飞。
有趣的是，化石记录清楚地表明，最早的鸟类并没有喙。但它们的许多兽脚类近亲都有喙，而且鸟类自身至少进化了两次喙，这表明这种转变非常容易。因此，成功飞上天空的秘诀之一，或许就在于拥有足够的胃。
附注：