GRE习题练习
| GRE考试易错题（2019/10/15） |
| 第1题：That large regions of the galaxy can be influenced by the formation of massive stars in a few localized regions requires that star formation somehow be coordinated over long periods of time. The process commences with a single O-type star or a cluster of such stars in a giant molecular cloud, around which stellar radiation, winds and explosions carve a modest cavity from of the surrounding interstellar medium, concomitantly destroying the progenitor clouD、Perchance this disturbance triggers star formation in a nearby cloud, and so on, until the interstellar medium in this corner of the galaxy resembles Swiss cheese, composed of what theorists have recently begun to refer to as bubbles, or superbubbles, one of the most exciting discoveries in astrophysics in years. Within a hot bubble, the sun has revealed itself in x-rays emitted by highly ionized trace ions such as oxygen and at some point in the process of its formation, nearby bubbles commence to overlap, coalescing into a superbubble. The energy from more and more O-type stars feeds this expanding superbubble until its natural buoyancy stretches it from the midplane up toward the halo, forming a chimney―the superbubble thus becomes a pathway for hot interior gas to spread into the upper reaches of the galactic atmosphere, producing a widespread coron A、Far from its source of energy, the coronal gas slowly starts to cool and condense into clouds. Over eons, these clouds fall back to the galaxy’’s mid-plane, completing the fountain-like cycle and replenishing the galactic disk with cool clouds from which star formation begins anew. Star formation often occurs in sporadic but intense bursts, but in the Milky Way the competing feedback effects almost balance out, so that stars form at an unhurried pace―just 10 per year on average, except in some galaxies where positive feedback has gained the upper hanD、20 million to 50 million years ago, star formation in the central parts of M82 began running out of control. Our galaxy, too, may have had sporadic bursts, and the way these starbursts occur, and what turns them off must be tied to the complex relation between stars and the tenuous atmosphere from which they precipitate. Progress will be made in this complicated subject as astronomers continue to study how the medium is cycled through stars, through the different phases of the medium, and between the disk and the halo. Observations of other galaxies give astronomers a bird’’s-eye view of the interstellar goings-on, and answer such a critical question as whether stars are really the main source of power for the interstellar medium. The loop above theCassiopeia superbubble1looks uncomfortably similar to the prominences that arch above the surface of the sun, prominences which owe much to the magnetic field in the solar atmosphere, and scientists have begun to wonder if magnetic activity dominates our galaxy’’s atmosphere. The primary function of the passage as a whole is to________. A、indicate the direction that research into a particular physical phenomenon should take B．illustrate the limitations of applying mathematics to complicated astrophysical phenomena C．clarify the differences between an old explanation of a physical phenomenon and a new model of it D．introduce a new explanation of a physical phenomenon E．explain the difference between two related physical phenomena |
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| 第2题： Perimeter,Area, and Volume These questions will test your knowledge of operations involving perimeter, area, and volume. Answer the following questions. |
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第4题：PRECIPITATE:
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| 第5题：The Headland Hypothesis argues that foraging or non-agricultural tribes have been unable to collect adequate carbohydrates in the rain forest due to its lack of starch producing species, and were thus forced to develop trade relationships with agriculturalists. This hypothesis has been shown to rest on impossibly idealized conceptions of virgin rain forest, forager behavior and history, such that one may argue something diametrically different: millennia of trade relationships with agricultural peoples have led to changes in forager behaviors and in the composition of the forests they inhabit. Supposing that humans modify their environments in ways that are generally favorable toward their continued survival, it follows that an increased reliance on agriculturalists for carbohydrates might lead to the gradual disappearance of rain forest starches. Horticulturalists are likely to dedicate the majority of their efforts toward staple starch crops such as rice or wheat, which in some environments may provide a more efficient source of carbohydrates than does foraging. Foragers, then, would be inclined to assume the "professional primitive" role, and trade more tasty and nutritious rain forest resources such as meat and fruit in exchange for carbohydrates, as Headland himself observed in a multitude of cultures around the worlD、Foragers may have also lost some of their knowledge and technologies related to carbohydrate extraction from the rain forest, and the carbohydrate-rich rain forest species may have arrested their co-evolution with foragers, leaving the impression that rain forests have always possessed insufficient quantities of such resources to support humans. A、co-evolutionary argument is not, however, necessary to this line of reasoning, for rain forests may adapt purely in terms of the quantity and availability of extant carbohydrate-rich species, as the case of sago palms evinces in two ways. Firstly, the selective harvesting of some trees has been shown to have a "thinning" effect which helps the species to gain sunlight and to thrive, positively affecting its long-term survival, reproduction and distribution at the expense of carbohydrate-rich species. Secondly, the sago palm has two means of reproduction: vegetatively, or through "suckers", and through seed disbursal, which whether intentional and inadvertent is likely to increase when humans are harvesting the trees.Although sago palms are particularlv nrevalent in the areas where, for instance the Penan foragers exploit it, there has been no study to show that this would remain the case if the Penan were to move, or to cease exploiting the trees. Admittedly, this response to the Headland Hypothesis has problems, for not all carbohydrate producing species are disbursed by seeds, nor have they all been shown to benefit from human foraging behaviors. Theories of co-evolution do, however, predict that such relationships would be likely to evolve, and the simple fact that disturbing the rain forest through fire, sago harvesting, and countless other means available to foragers can lead to better environments for carbohydrate growth, illustrates that significant changes could have occurred in much less time than one might expect.The author of the passage mentions which of the following as posing an alternative to the Headland Hypothesis A、Rain forests have always possessed insufficient quantities of carbohydrate-rich resources to support foragers without the aid of agriculturalists. B．The difficulty of raising carbohydrate-rich plant species in certain areas of the rain forest may have led to the arrest of those species’’ co-evolution. C．Trade relationships between agriculturalists and foragers may have been the cause of the disappearance of certain carbohydrate-rich plant species, not vice-vers A、 D．Foragers may have been willing to trade carbohydrate-rich plants in exchange for the more nutritious food products of agriculturali |
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