Despite a tendency to be overtly _______, the poetry of the Middle Ages often sparks the imagination and provides lively entertainment, as well as pious sentiments.

阅读理解Women s roles in literature nave not evolved nearly as rapidly as women'' s changing roles in society, and while these changes are reflected somewhat in what is written, female characters in most classic literature written by both men and women seem to adhere to the classic stereotypes. Though writing during an era in which impersonal criticism was virtually the only way for a woman to maintain objectivity, Virginia Woolf protested the notion that authors ought to separate fiction from reality, and her imaginative use of drama and character development to establish her point can be evidenced in her feminist non-fiction, most prominently the battle against patriarchal authority. Owing to its numerous personal references, most critics have claimed that her oeuvre is somehow self-centered or egotistical rather than objective, yet in truth Woolf is not using her personal experiences as a means with which to reflect upon her own self-image, but rather as a way to more vibrantly illustrate her external perceptions.

阅读理解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.

阅读理解As the political consequences of Nazism and the liberal tone of the postwar world proved inhospitable to Darwinist thinking, so the disintegration of the postwar order, the end of traditional leftwing politics, a growing social conservatism and disillusionment with the idea of social progress has led to its return. As anthropologist Foley expounded, the history of the twentieth century has transformed our vision of humanity, leading to a loss of confidence in the notion that humans may be raised on a taxonomical pedestal above the swamp of animal brutishness. In deriding any social explanation of human behavior, and implying that emotions are biologically shaped, hence universal, scientists have come to odds with cultural anthropologists, who ridicule any biological interpretation of human behavior and view humans in strictly cultural terms. There is convincing evidence that the anthropologists are correct, for even something as fundamental as an emotion is far more than simply an evolutionary trait, given that only some emotions--anger, disgust, sadness, enjoyment and fear--are known to be universal, while others, such as jealousy and envy, vary in their expression and are arguably not emotions at all. Even emotions known to be universal cannot be regarded as simply "natural", given that the evocation of a particular emotion is both culturally and historically specific. The connotation of anger or sadness and the elicitors of these emotions may vary across cultures and throughout human history. There.are also culturally bound "display rules", often unconscious, which dictate the means or time of displaying emotion. For instance, Japanese and American students are privately shown very similar emotions in response to similar stimuli, but their public expressions are far from identical, a fact that may owe to the Japanese cultural tendency of remaining demure in public expression. 　　Even more contentious is the question of what emotions animals possess, of whether they are aware of such emotions, and of the relationship between animal responses and human emotions. The way of responding to these debates depends as much upon one''s philosophical inciinations as on the facts: scientists philosophically disposed to minimize the gap between humans and animals are more likely to perceive animals as having emotions, as being aware of them, while those anthropologists who seek an unbridgeable gap between humanity and lower life forms are likely to see appreciable differences between human emotions and animal responses. Thus, the scientific idea of the human is not simply an objective truth, but shaped by wider issues such as the prevailing ideas of progress, notions of racial difference, and the comprehension of the relationship between Man and Nature. All that may safely be concluded is that what constitutes a human is not only innate, but also nurtured.

阅读理解Economics can render service in the area of exchange, but its tools find less purpose when applied to paradigms dominated by alternative models of transactions and social relationships. In small groups gift-giving is substituted Line for the role of exchange, which entails obligation: people receiving gifts are expected to reciprocate in the future and this reciprocity binds small groups together, whereas exchange rarely does so. Two people exchange only when both benefit, neither incurring a social obligation as a result, and where social obligations exist, exchange may not work well. Exchange nevertheless allows for extremely complex interactions among strangers: when employing a product, a consumer benefits from the efforts of hundreds of anonymous people who have contributed to that commodity. Such analysis also has its limits in the case of an area such as government, for economics seeks regularities in social life, which are more likely to occur when no one individual has an appreciable effect on the group.

阅读理解One reason why a sheep, a less well-understood experimental subject than the laboratory mouse, should have proved easier to clone may stem from differences in the initial stages of the two species'' embryonic development. After reaching maturity in the ovary of the mother, the unfertilized eggs of all mammals accumulate a supply of proteins, and the means of producing fresh protein. In this way, the mammalian egg brings with it a larder for the embryo to make use of until its own genes activate and supply this requirement themselves. The sheep embryo disposes of its store properly and need not depend on its own genes until the sixteen-cell stage, four cell divisions successive to fertilization, while in contrast, the mouse embryo commences this process more precociously, becoming reliant on the activity of its own genes after just the first division when the fertilized egg becomes two cells. Therefore, a foreign nucleus introduced into a sheep egg exploits a respite in its host''s biological development, allowing it to adapt to its new role before assuming genetic control. 　　Concomitantly, a nucleus introduced into a mouse egg must acclimatize quickly for its genes to be able to direct embryonic development within a single cell division, so perhaps there is insufficient time for the extensive re-programming of compulsory gene activity. The human embryo is thought to rely on its own genes after three cellular divisions, which might or might not provide time enough for a foreign nucleus to acclimate. However, were scientists to comprehend the nature of the indispensable re-programming then there is every likelihood that both mice and humans could be cloned. 　　Despite the long-standing availability of this technology, there has until recently been little interest in it. Some people suffering from infertility as a result of rare hereditary diseases could produce offspring, but cloned individuals may be at risk given scientists'' limited knowledge of the long term effects of allowing an "old" adult cell nucleus to commence life again in an egg. The nucleus of a skin cell could have accumulated a multitude of genetic mistakes of no consequence to its role in the skin, but the same cell could prove deleterious in other tissues, or immensely increase the probability of the affliction with cancer. The threat to general human health posed by cloning, as opposed to the individual, is difficult to determine, but the risks are almost certainly lower than those encountered in the effective inbreeding of consanguine marriages, and thus there are no scientific grounds per se for banning cloning. Like other practices inconsequential to the physical well being of humanity, but generally deemed undesirable on moral or social grounds, the prohibition of human cloning will ultimately rest with only a simple pragmatic decision.

阅读理解Previously, the sack-like rabbit appendix was thought to serve primarily as a reservoir for the bacteria involved in hindgut fermentation, a explanation that failed to account for the absence of an appendix in other animals with similar digestive systems or for its presence in humans. Microscopic research revealed that the appendix contains a significant amount of lymphoid tissue, similar aggregates of which tissue occur in other areas of the gastrointestinal tract. These are involved, possibly, in the body''s ability to recognize foreign antigens in ingested material, but the evidence is inconclusive, to the extent that scientists have long discounted the human appendix as a "vestigial" organ. However, a growing body of evidence suggests that the appendix, far from being a "vestigial organ", hag a significant function as a part of the body'' s immune system. The appendix achieves its greatest development shortly after birth, when immune response is first developing, then regresses with age, when the immune response mediated by the appendix may relate to such inflammatory conditions as ulcerative colitis, which in adults necessitates the organ'' s surgical removal.

阅读理解McClary''s position, concerning the process by which music is gendered as masculine or feminine, is that socially-grounded codes are "composed into" the music, that they are immanent to the text, there to be discovered. McClary has traced narratives of power and sexual differences in sonata forms by mapping the gendered terms in which theorists have described them onto pieces which variously appear to enact or resist such constructions. 　　Rieger has likewise traced the inchoate differentiation of musical affects by gendered characters in late-eighteenth-century opera, and charted their much heightened divergence in contemporary film music. Both of these approaches　share a common assumption of a degree of awareness of such gendered codes at the point of composition, an awareness which, if not fully reflective, at least shows a composer''s "practical consciousness" of how musical expression works　within his or her culture. This conception permits music to participate fully in cultural processes, thereby allowing us to bring cultural contexts to bear in our　explanatory models of musical styles and forms, but its critics rightly argue that it carries an extreme risk: it is all too easy for this approach to re-inscribe the values it would aim to critique. We may accuse McClary of adopting the very　stereotypes she deplores, and similarly we may regard her identification of musical difference with cultural difference to be an overinterpretation, though　unless we limit our focus to some extreme of the avant-garde, we must concede that some kind of contrast between masculinity and femininity will always exist in any music. 　　It is perhaps best to argue the possibility that such gender metaphors are merely functions of our interpretational frameworks, imposed on music from the outside. Treitler describes the way in which scholars from the eighteenth to the twentieth centuries have differentiated between Old Roman and Gregorian chant repertories in gendered terms, and argues that these metaphors relate entirely to a project of Western cultural supremacy, and not to any immanent musical characteristics of the actual chants. We may make the same point about all repertories: gender is encoded not in the music, but in the critical language we use, much like Pigmalion''s chisel, to bring the music to life. While this position is weaker than McClary''s in an explanatory capacity―it cannot use social values to account for why a piece was written the way it was rather than any other, aesthetically speaking--its value is ultimately greater in that it allows us to develop fresh listening strategies which invest familiar and well-loved music with new and arguably more positive values. Hence, it is more attractive for the development of a politically responsible critical strategy, though even in this respect, the position is not without shortcomings, most of which become apparent when we examine the relationship between musical　material and cultural meaning.

阅读理解Crosby''s recent study of American historical demography is blithely based on the reconstitution of the records of single parishes, a method that often excludes migrants. Moreover, it is troublesome for historians to obtain information on the birthdates of people who relocated to the parish, and equally difficult to follow those who had migrated to new places of residence. Thus, the exclusion of migrants also followed from the way spatial units were once conceived by the parishioners themselves, a stable and unchanging pre-modern countryside of interchangeable towns unlike "modern" flows to cities. 　　As a result, migration was improperly assumed to be irrelevant because the small units in the countryside were interchangeable and migrants into a parish could thus stand as a proxy for those who had left. In any case, it was thought that migration in the countryside was repetitive and occurred only in response to life course events, such as finding a spouse, and thus, like the parishioners themselves, Crosby complacently equates the demographics of migrants to those of more sedimentary populations.

阅读理解Most words are "lexical words", i.e. nouns signifying "things", the majority of which are abstract concepts rather than physical objects in the world; only "proper nouns" have specific and unique referents in the everyday world. The communicative function of a fully-functioning language requires the scope of reference beyond the particularity of the individual instance. While each leaf, cloud or smile is different from all others, effective communication requires general categories or "universals". Anyone who has attempetd to communicate with people who do not share their language will be familiar with the limitations of simply pointing to things, given that the vast majority of lexical words in a language exist on a high level of abstraction and refer to classes of things such as "buildings" or to concepts like "construction". 　　We lose any one-to-one correspondence of word and thing the moment we group instances into classes. Other than lexical words, language consists of "function words" or grammatical words, such as "only" and "under" which do not refer to objects in the world at all, and many more kinds of signs other that simple nouns. The notion of words as labels for concepts assumes that ideas exist independently of words and that ideas are established in advance before the introduction of linguistic structure. Clearly, language is not limited to naming things existing in the physical world, but includes non-existent objects and ideas well.　The nomenclaturist stance, in viewing words as labels forpre-existing ideas and objects, attempts unsuccessfully to reduce language to the purely referential function of naming things. Things do not exist independently of the sign systems which we use; "reality" is created by the media which seem simply to represent it. Language does not simply name pre-existing categories; categories do not exist in "the world" . e. g. "where are the boundaries of a cloud; when does a smile begin". Such an emphasis on reality as invariably perceptually seamless may be an exaggeration; our referential categories do seem to bear some relationship to certain features which seem to be inherently salient. Within a language, many words may refer to "the same thing" but reflect different evaluations of it. For example, ''one person''s ''hovel'' is another person''s '' home''" 　　Meanwhile, the signified of a word is subject to historical change. In this sense, "reality" or "the world" is created by the language we use: this argument insists on the primacy of the signifier. Even if we do not adopt the radical stance that "the real world" is a product of our sign systems, we must still acknowledge the lack of signifiers for many things in the empirical world and that there is no parallel correlation between most words and objects in the known world at all. Thus, all words are "abstractions", and there is no direct correspondence between words and "things" in the world.

阅读理解Scientists studying the effect of large volcanic eruptions on global climate have long focused on the major quantities of carbon dioxide (C02), a gas known to contribute to the greenhouse effect, produced by these eruptions. It is well observed that such greenhouse gases trap heat radiated from the surface of the earth, thereby forming a type of insulation around the planet. The greenhouse effect is essential for ecological equipoise because it maintains the temperature of the planet within habitable parameters, but there is growing concern that man-made production of gases such as CO[,2] from the burning of fossil fuels may be threatening the system''s tolerance, and have resulted in excessive warming on a global scale. While volcanic eruptions indubitably metabolize and accumulate C0[,2] in the atmosphere, it has been recently discovered that their impact is virtually trivial compared to the quantity produced by human activities, especially heavy industry. In reality, the more substantive climatic effect from volcanoes results from the production of atmospheric haze, whereby large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere, clouds that circumscribe the globe within weeks of the volcanic activity. Ash and aerosol clouds from large volcanic eruptions disseminate quickly through the atmosphere, and the small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures, while the sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space. 　　There is evidence that volcanoes'' stratospheric ash clouds has a lesser effect on global temperatures than aerosol clouds, given that the major Mt. St. Helens eruption had lowered global temperatures by about 0.1 degree C, while two years later the much smaller eruption of El Chico had, by contrast, three to five times the global cooling effect worldwide. Despite its smaller ash cloud, El Chico emitted more than 40 times the volume of sulfur-rich gases produced by Mt. St. Helens, revealing that the formation of atmospheric sulfur aerosols has a more substantial effect on global temperatures than simply the volume of ash produced during an eruption. Sulfate aerosols appear to necessitate several years to settle out of the atmosphere, one of the reasons their effects are so widespread and enduring. This corroborates the opinion of those scientists who argue that without the cooling effect of major volcanic eruptions such as El Chico, global warming effects caused by human activities would be far more substantial. It should be noted that major volcanic eruptions have additional climatic effects beyond global temperature decreases and acid rain, for ash and aerosol particles suspended in the atmosphere scatter light of red wavelengths, often resulting in brilliantly colored sunsets and sunrises around the world.

阅读理解Since her own era, Christina Rossetti''s devout Christianity has often been seen as a characteristic setting her apart from the other avowedly non-Christian members of the Pre-Raphaelite circle. In designating their movement a form of"aesthetic mysticism", one established critic, Alice Law described the place Pre-Raphaelitism holds in the development of Victorian artistic culture as a movement away from a predominantly religious and moralizing function toward a culture of aestheticism―precisely what Rossetti''s work has long been thought to reject. The Pre-Raphaelites'' attention to picturesque detail, the medievalist atmosphere and settings, the pervasive melancholy of their works, and their awareness of their art''s primarily Christian literary and pictorial origins―all these have been traditionally downplayed in their similarity to the characteristics of Christina Rossetti''s poetry. 　　This belief persists, despite the distinctly religious "atmosphere" of much of the work produced by both generations of Pre-Raphaelites: its employment of biblical images and typology; of religious figural language; and, more especially and pervasively, of medievalist backgrounds and settings that were seen by their early audiences to have clearly devotional, if not dangerously "Romanist", associations. When discussing Pre-Raphaelitism as an historical movement, we must remember that the first brotherhood was inspired largely by a sacramental aesthetic that tended to alienate Victorian society, which generally abhorred the notion of sacrifice. It is true that Rossetti''s traditional solution to the Romantic and Victorian literary problem of alienation from nature and the more characteristically Victorian problem of despair at life''s meaninglessness, was fundamentally Christian. But with few exceptions, Rossetti relied on the colloquial and angst-ridden language of both generations of Pre-Raphaelites. Even Swinburne, the Pre-Raphaelite whose anti-orthodoxy and iconoclasm seem to conflict most profoundly with Rossetti''s values, enthusiastically hailed her. 　　That most Victorians themselves perceived Christina Rossetti as unequivocally Pre-Raphaelite in her poetic affinities is clear, for throughout her poetry and much of her prose Christina Rossetti demonstrated true and deep affinities with Pre-Raphaelite aesthetic values, in both innovative and traditional ways. We must not forget her "pictorial" modes of representation, the medieval atmosphere and settings that appear repeatedly in her poems, her appreciation of the world''s physical beauty and its expression in lush images, the intensity of her poems, which seems inseparable from their "sincerity", and not least her preoccupation with love. To a greater extent than figures more peripheral to the Pre-Raphaelite circle, Christina Rossetti produced works that appear to be dominated by the same aesthetic consciousness and literary values that make Pre-Raphaelitism the central movement which unintentionally spawned the aestheticism of the 1880s and 1890s. Pre-Raphaelitism, in fact, influenced aesthetic thought in a way that made the movement central to the transition from the sentimental moral idealism of the Victorian mainstream to the variously nihilistic, skeptical, and ironic value systems that dominate modern poetry.

阅读理解Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on Earth in comparison with the age of Mars, an enigma exarcebated by the fact that the Martian rocks were ejected Line by only six or seven separate impact events. Previous tests had predicted that driving meteorites to Earth would require a collision with an asteroid immense enough to make a crater 12-kilometers across, but because such huge impacts are extremely infrequent, it was unlikely that enough of them could have occurred to explain our planet''s Martian meteorite collection. Now astronomer James Head''s higher-resolution models demonstrate that collisions making craters only three kilometers across can jettison 10 million fragments, each about 10 centimeters across, into space, a distribution sufficient to cause some of them to be found on Earth. Sections of the planet covered by debris (thus likely to be made up of older terrain) would require larger and hence rarer impacts, and thus meteorites which reach Earth are predictably biased toward younger ages.Scientists have long sought the reasons for the relatively young age of the majority of Martian meteorites discovered on Earth in comparison with the age of Mars, an enigma exarcebated by the fact that the Martian rocks were ejected Line by only six or seven separate impact events. Previous tests had predicted that driving meteorites to Earth would require a collision with an asteroid immense enough to make a crater 12-kilometers across, but because such huge impacts are extremely infrequent, it was unlikely that enough of them could have occurred to explain our planet''s Martian meteorite collection. Now astronomer James Head''s higher-resolution models demonstrate that collisions making craters only three kilometers across can jettison 10 million fragments, each about 10 centimeters across, into space, a distribution sufficient to cause some of them to be found on Earth. Sections of the planet covered by debris (thus likely to be made up of older terrain) would require larger and hence rarer impacts, and thus meteorites which reach Earth are predictably biased toward younger ages.

阅读理解Air turbulence can substantially accelerate the appearance of large dropletstriggering rain by presenting a new mechanism, the "sling effect", which increases collisions of droplets that have become detached from the airflow. First, vapor condensation in cloud cores produces small droplets resembling one another in size, which then expand to raindrop size by coalescing under the effects of air turbulence―a force thought to cause collisions of similar-sized droplets whose radii exceed a few micrometers. Then, turbulent vortices act as small centrifuges that spin heavy droplets out, creating concentration heterogeneities and jets of droplets, both of which increase the mean collision rate, which in turn accelerates rain initiation. 　　One can conclude that rain prediction requires a quantitative description of droplet collision in turbulence, a mechanism which helps meteorologists to forecast rainfall, but detailed understanding of the phenomenon entails consideration of such factors as warm and cold fronts stretching over hundreds of miles, individual clouds perhaps a mile or so across, and even, as the mechanism illustrates, tiny eddies perhaps a few centimeters or so in size.

阅读理解Hitherto, there is no evidence yet that would definitively prove whether or not some dinosaurs were warm-blooded, but scientists have begun to investigate　oxygen isotopic abundances in the annual growth bands of teeth or bones of high Line latitude, hence seasonally influenced, terrestrial dinosaurs. The ratio of oxygen isotopes depends on temperature, and an absence of seasonal variations in oxygen 18―a heavy version of the common oxygen 16 atom―would　strongly suggest that the animals maintained a constant internal　temperatures. Such a finding would not, however, constitute "proof"　that dinosaurs were warm blooded, as there are external mechanisms that cold-blooded animals employ to　regulate body temperatures and thereby influence metabolic rates. More nettlesome is that proof would have to come from discovery of intact dinosaur remains in which the soft tissue had not been replaced or altered, and from which the biomolecules responsible for thermoregulation could be extracted identified and characterized. Such a proof is unlikely, as it would require an　almost impossible level of preservation over 65 million years, plus the advent of biotechnology that does not yet exist.

阅读理解Carl Jung''s well-documented break with Sigmund Freud occurred because of Jung''s inability and unwillingness to accept Freud''s view of the libido as the sexual drive of fulfillment. Believing that the libido, or the urge towards life, extended beyond mere sexuality to a hypothetical elan vital, or life energy itself, Jung stressed a widened consciousness whereby the individual seeks to reconcile the opposites of his or her libidial nature that dwell in the conscious as well as the personal and collective unconscious. 　　Jung defines this consciousness, moreover, as the center of the ego, and the personal unconscious as a repository of repressed personal experiences or complexes that must be made conscious. Finally, the collective unconscious is an archive of hereditary symbolic archetypes that express themselves in dreams, fantasies, and actions, and must also be made conscious. Jung postulated that these archetypal patterns must be integrated into the world of the ego, which is then forced to acknowledge for these reasons that the egocentered consciousness is not really self-sufficient and does not exist independently and alone, but is guided by an integrating factor not of its own making.

阅读理解Hydrothermal vents along the mid-ocean ridges host ephemeral ecosystems of diverse fauna, including several crustacean species, some of which undergo development as larvae up to 1,000 meters above and 100 kilometers away from the vents. For example, vent crab Bythograea thermydron (at stage of larvae) possess image-forming compound eyes with a visual pigment sensitive to the blue light of upper oceanic waters. As these larvae metamorphose into adulthood and begin to descend to and settle at the vents, they lose their imageforming optics and develop highsensitivity naked-retina eyes. With maturation,the spectral absorbance of the visual pigment in these eyes also shifts towards longer wavelengths and this progressive visual metamorphosis trades imaging for increased sensitivity, and changes spectral sensitivity to the dim, longer wavelengths of light existing at the bottom of the ocean. As hydrothermal vents produce light, vision may supplement thermal and chemical senses to orient post-larval settlement at vent sites.

阅读理解Given that 8 percent of food crops grows faster on farms using groundwater than the aquifers are replenished, and many large rivers are so heavily diverted that they do not reach the sea for much of the year, researchers believe freshwater sources--underground aquifers and rivers--are stressed. Better management of soil and water and creative cropping patterns can boost production from rainfall-watered cropland, but the heaviest burden will fall on irrigated land. At present, most farmers irrigate their crops by channeling water down their fields in parallel furrows. 　　One alternative, drip systems, enables farmers to deliver water directly to the plants'' roots drop by drop, nearly eliminating waste by distributing water at low pressure through a network of perforated plastic tubing installed on or below the surface of the soil, where it then emerges through small holes at a slow but steady pace. Because the plants enjoy an ideal moisture environment, drip irrigation usually offers the added bonus of higher crop yields. Another alternative, sprinklers, can perform almost as well as drip methods when designed properly, but traditional high-pressure irrigation sprinklers spray water high into the air to cover as large a land area as possible, and the more time the water spends in the air, the more of it evaporates before use. 　　Despite the payoffs, the higher costs of these technologies relative to simple flooding methods have been a barrier to their spread, and so has the prevalence of national water policies that discourage rather than foster efficient water use. Many governments have set very low prices for publicly supplied irrigation, leaving farmers with little motivation to invest in ways to conserve water or to improve efficiency and most authorities have also failed to regulate groundwater pumping, even in regions where aquifers are over-tapped. Therefore, farmers might be inclined to conserve their own water supplies if they could profit from selling the surplus, but this practice is often discouraged. 　　Efforts aside from irrigation technologies are also conducive to the reduction of agricultural demand for water; for instance, measurements of climate factors such as temperature and precipitation can be fed into a computer that calculates how much water a typical plant is consuming, and farmers can use this figure to determine, quite accurately, when and how much to irrigate their particular crops throughout the growing season. But the most effective, if unlikely way, to do more with less water is to reconfigure our diets, especially the typical North American diet, which, with its large share of animal products, requires twice as much water as diets common in many Asian and some European countries. Eating lower on the food chain could allow the same volume of water to feed two Americans instead of one, and despite the resultant loss of nutrition, this may be the only recourse for countries serious about reducing their aquifer strain.

阅读理解Homeostasis refers to any process, such as negative feedback, that living things employ to maintain stable conditions indispensable for survival, and which arises from balances between forces and factors mutually influencing each other. Disturbance, or departure from equilibrium is of more consequence than negative feedback: systems cannot correct themselves without straying. A car and its driver, for instance, can be regarded as a homeostatic system seeking to keep the car moving on track. Thus, if the car skids, the driver automatically responds by quickly steering the wheel in the opposite direction, but such abrupt negative feedback usually overcorrects. Likewise, if the magnitude of correction is commensurate with the disturbance that triggered it, the correction may become an impressed change in the direction opposite to that of the original disturbance. Each feedback is of lesser magnitude than the last, so that as the oscillations of the system dampen, negative feedback achieves its goal in both artificial and natural systems.

阅读理解While examination of Eisenstein'' s work has yielded better understandings of film theory, such attention is rarely granted to the work of his successors. Even within the comparatively specialized field of film studies, these films remain largely ignored; they are discussed in a reductive and superficial manner when taught, typically valued solely for rejecting or contesting Hollywood norms, trivializing movements sorely in need of rejuvenation, and given the economic situation of independent film production, such ignorance generates a destructive cycle of neglect and ignorance. The stakes involved in naming Eisenstein as the model of the modernist film project are especially fraught since the values implicit in such a decision help determine the availability of entire bodies of radical film. One deleterious result of applying the "Eisenstein standard" has been to make it easier than ever to remain ignorant of experimental film forms, which can uniformly be extolled as "transgressive" or "deconstructive" without serious engagement.