试题库在线考试题库-历年真题模拟试题及答案-考博英语在线试题测试中心-希赛网

华中科技大学

The airline will also recycle paper cups and plastic bottles, and use chopsticks produced from wood from forest thinning projects, as part of its efforts to become more environmentally friendly. The measures are being trialed on 38 domestic flights and four international flights—on the Tokyo-Singapore route—during October.

根据《自然神经科学》杂志的报道，那些在夏天的光照条件下成长起来的老鼠像往常一样作息，而那些在缺少光线的环境中成长起来的老鼠在应对这一变化时却显得吃力。研究者道格拉斯•麦克马洪教授说：“在冬天的光照周期中成长起来的老鼠对于季节的变化表现出夸大的反应，这和得了季节性情感抑郁症的人类病患的反应极其相似。”

有些老鼠被放置在夏天的光照条件下，每天有16小时的“白天”和8个小时的“黑夜”。其他老鼠则只有8个小时的“白天”，和冬天昼短夜长的光照条件类似。在这些老鼠断奶后，它们被放置在相同的光照周期中长达数周，或转换到相反的光照环境。最后，科学家把它们都放置到黑暗中，观察它们的反应。

Astrophysicists wrestling with the study of a new kind of star, the flat, “two-dimensional” configurations known as accretion disks have recently gained new insights into the behavior of these stars. Accretion disks exist in a variety of situations where matters swirl around a compact star such as a white dwarf star or a neutron star. Accretion disks are also suspected of playing a part in more exotic situations, in which the central object is imagined to be a supermassive black hole, the ultimate form of collapsed matter, rather than a compact star. The modeling of accretion disks is still in its infancy, a situation analogous to the days when ordinary stars were modeled by using elementary scaling laws without benefit of knowledge of the nuclear processes that power the stars. Similarly, the basic physics of the power by which accretion disks radiate, thought to originate in a form of turbulent friction, is known only at the crudest level.Accretion disks were first defined in the context of Cataclysmic variables. In these systems, matter from the outer layers of an ordinary star is attracted by the gravitational influence of a nearby orbiting white dwarf star, the matter lost from the ordinary star cannot strike the surface of the tiny white dwarf directly but settles into an orbit around the star. The viscosity in the disk thus formed causes heating, radiation, and a slow spiraling of disk matter onto the surface of the white dwarf.The rapid advances made in x-ray astronomy in the past decade have identified a second type of system in which accretion disks occur. In such a system, an accretion disk whirls about a neutron star rather than a white dwarf. The inner reaches of the accretion disk extend deeply into the gravitational potential of the neutron star where very rapid motion is the rule. The energy released by friction and the actual raining of the material from the disk onto the surface of the neutron star is so great that radiation is given off in a powerful flood of x-rays. And in at least one case, x-ray astronomers believe that the object in the center of an accretion disk is a black hole, suggesting that a third system may exist.It had been assumed that portions of accretion disks would be unstable and that, as a result, clumping of their matter into rings would occur. There is no evidence from observation, however, that accretion disks do, in fact, suffer from these instabilities. In recent work, Abramowicz has shown that added gravitational effects due to general relativity may alter the expected Newtonian gravitational relationships in such a way that the disk remains stable, indicating that it is possible that these predicted instabilities do not occur.Further progress toward understanding accretion disks will involve defining and proposing solutions to restricted problems just as was done in this case and was done and continues to be done for ordinary stars. Abramowicz' work is a valuable example of the care that must be taken before reaching conclusions regarding accretion disks.1.The author of the passage is primarily concerned with（）.2.It can be inferred from the passage that predictions of the instability of accretion disks were based on which of the following?3.The author’s attitude toward Abramowicz’ work can best be described as one of（）. 4.The passage suggests which of the following about current scientific knowledge of the nuclear processes of ordinary stars?5.The passage suggests that Abramowicz’ work was motivated by which of the following assumptions?6.The passage implies which of the following about the progress of knowledge in astrophysics?7.The passage suggests that, compared to the study of ordinary stars, the study of accretion disks is（）. 8.According to the passage, some accretion disks originated in（）. 9.It can be inferred from the passage that the significance of Abramowicz’ work is that it（）.

Agricultural progress provided the stimulus necessary to set off economic expansion in medieval France. As long as those who worked the land were barely able to ensure their own subsistence and that of their landlords, all other activities had to be minimal, but when food surpluses increased, it became possible to release more people for governmental, commercial, religious and cultural pursuits.However, not all the funds from the agricultural surplus were actually available for commercial investment. Much of the surplus, in the form of food increases, probably went to raise the subsistence level; an additional amount, in the form of currency gained from the sale of food, went into the royal treasury to be used in waging war. Although Louis VII of France levied a less crushing tax burden on his subjects than did England’s Henry II, Louis VII did spend great sums on an unsuccessful crusade, and his vassals—both lay and ecclesiastic—took over spending where their sovereign stopped. Surplus funds were claimed both by the Church and by feudal landholders, whereupon cathedrals and castles mushroomed throughout France.The simultaneous progress of cathedral building and, for instance, vineyard expansion in Bordeaux illustrates the very real competition for available capital between the Church and commercial interests; the former produced inestimable moral and artistic riches, but the latter had a stronger immediate impact upon gross national product. Moreover, though all wars by definition are defensive, the frequent crossings of armies that lived off the land and impartially burned all the huts and barns on their path consumed considerable resources.Since demands on the agricultural surplus would have varied from year to year, we cannot precisely calculate their impact on the commercial growth of medieval France. But we must bear that impact in mind when estimating the assets that were likely to have been available for investment. No doubt castle and cathedral building was not totally barren of profit (for the builders, that is), and it produced intangible dividends of material and moral satisfaction for the community. Even wars handed back a fragment of what they took, at least to a few. Still, we cannot place on the same plane a primarily destructive activity and a constructive one, nor expect the same results from a new bell tower as from a new water mill. Above all, medieval France had little room for investment over and above the preservation of life. Granted that war cost much less than it does today, that the Church rendered all sorts of educational and recreational services that were unobtainable elsewhere, and that government was far less demanding than is the modern state—nevertheless, for medieval men and women, supporting commercial development required considerable economic sacrifice.1.According to the passage, agricultural revenues in excess of the amount needed for subsistence were used by medieval kings to（）.2.According to the passage, which of the following was an important source of revenue in medieval France?3.The passage suggests that which of the following would have reduced the assets immediately available for commercial investment in medieval France?I. Renovation of a large cathedral.II. A sharp increase in the birth rate.III. An invasion of France by Henry II.4.It can be inferred from the passage that more people could enter government and the Church in medieval France because（）. 5.The author implies that the reason we cannot expect the same results from a new bell tower as from a new water mill is that（）. 6.The author of the passage most probably bases his central argument on which of the following theoretical assumptions often made by economists?7.The author suggests that commercial expansion in medieval France “required considerable economic sacrifice” (lines 59-60) primarily for which of the following reasons?8.The passage implies that which of the following yielded the lowest dividend to medieval men and women relative to its cost?9.Which of the following statements best expresses the central idea of the passage?

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