[考研类试卷]考研英语(阅读)模拟试卷81及答案与解析.doc
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1、考研英语(阅读)模拟试卷 81 及答案与解析Part ADirections: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)0 In the following article, some sentences have been removed. For Questions 1 5, choose the most suitable one from the list AG to fit into each of the numb
2、ered blank. There are two extra choices which you do not need to use.Until about two million years ago Africas vegetation had always been controlled by the interactions of climate; geology, soil, and groundwater conditions; and the activities of animals. The addition of humans to the latter group, h
3、owever, has increasingly rendered unreal the concept of a fully developed “natural“ vegetationi. e. , one approximating the ideal of a vegetational climax. 【R1】_. Early attempts at mapping and classifying Africas vegetation stressed this relationship: sometimes the names of plant zones were derived
4、directly from climates. In this discussion the idea of zones is retained only in a broad descriptive sense.【R2 】_. In addition, over time more floral regions of varying shape and size have been recognized. Many schemes have arisen successively, all of which have had to take views on two important as
5、pects; the general scale of treatment to be adopted, and the degree to which human modification is to be comprehended or discounted.【R3 】_. Quite the opposite assumption is now frequently advanced. An intimate combination of many speciesin complex associations and related to localized soils, slopes,
6、 and drainage has been detailed in many studies of the African tropics. In a few square miles there may be a visible succession from swamp with papyrus, the grass of which the ancient Egyptians made paper and from which the word “paper“ originated, through swampy grassland and broad-leaved woodland
7、and grass to a patch of forest on richer hillside soil, and finally to juicy fleshy plants on a nearly naked rock summit.【R4 】_. Correspondingly, classifications have differed greatly in their principles for naming, grouping, and describing formations; some have chosen terms such as forest, woodland
8、, thorn-bush, thicket, and shrub for much of the same broad tracts that others have grouped as wooded savanna(treeless grassy plain)and steppe(grassy plain with few trees). This is best seen in the nomenclature, naming of plants, adopted by two of the most comprehensive and authoritative maps of Afr
9、icas vegetation that have been published; R. W. J. Keays Vegetation Map of Africa South of the Tropic of Cancer and its more widely based successor, The Vegetation Map of Africa , compiled by Frank White. In the Keay map the terms “savanna“ and “steppe“ were adopted as precise definition of formatio
10、ns, based on the herb layer and the coverage of woody vegetation; the White map, however, discarded these two categories as specific classifications. Yet any rapid absence of savanna as in its popular and more general sense is doubtful.【R5 】_. However, some 100 specific types of vegetation identifie
11、d on the source map have been compressed into 14 broader classifications.AAs more has become known of the many thousands of African plant species and their complex e-cology, naming, classification, and mapping have also become more particular, stressing what was actually present rather than predicti
12、ng climatic potential.BIn regions of higher rainfall, such as eastern Africa, savanna vegetation is maintained by periodic fires. Consuming dry grass at the end of the rainy season, the fires burn back the forest vegetation, check the invasion of trees and shrubs, and stimulate new grass growth.COnc
13、e, as with the scientific treatment of African soils, a much greater uniformity was attributed to the vegetation than would have been generally accepted in the same period for treatments of the lands of western Europe or the United States.DThe vegetational map of Africa and general vegetation groupi
14、ngs used here follow the White map and its extensive annotations.EAfrican vegetation zones are closely linked to climatic zones, with the same zones occurring both north and south of the equator in broadly similar patterns. As with climatic zones, differences in the amount and seasonal distribution
15、of rainfall constitute the most important influence on the development of vegetatioaFNevertheless, in broad terms, climate remains the dominant control over vegetation. Zonal belts of rainfall, reflection latitude and contrasting exposure to the Atlantic and Indian oceans and their currents, give so
16、me reality to related belts of vegetation.GThe span of human occupation in Africa is believed to exceed that of any other continent. All the resultant activities have tended, on balance, to reduce tree cover and increase grassland)but there has been considerable dispute among scholars concerning the
17、 natural versus human-caused development of most African grasslands at the regional level.1 【R1 】2 【R2 】3 【R3 】4 【R4 】5 【R5 】5 In the following article, some sentences have been removed. For Questions 1 5, choose the most suitable one from the list AG to fit into each of the numbered blank. There ar
18、e two extra choices which you do not need to use.Between 5,000 million and 4,000 million years ago the Earth was formed. By 3,000 million years ago life had arisen and we have fossils of microscopic bacteria-like creatures to prove it. 【R1】_. Nobody knows what happened, but theorists agree that the
19、key was the spontaneous arising of self-duplicating entities, i. e. something equivalent to “genes“ in the general sense.The atmosphere of the early Earth probably contained gases still abundant today on other planets in the solar system. Chemists have experimentally reconstructed these ancient cond
20、itions in the laboratory. If plausible gases are mixed in a container with water, and energy is added by an electric discharge(simulated lightning), organic substances are spontaneously synthesized. These include the building blocks of RNA and DNA. It seems probable that something like this happened
21、 on the early Earth. Consequently, the sea would have become a “soup“ of prebiological organic compounds. 【R2】 _.Today the most famous self-duplicating molecule is DNA, but it is widely thought that DNA itself could not have been present at the origin of life because its duplication is too dependent
22、 on support from specialized machinery, which could not have been available before evolution itself began. Perhaps the related molecule RNA, which still plays various vital roles in living cells, was the original self-duplicating molecule. Or perhaps the earliest duplicator was a different kind of m
23、olecule altogether. 【R3】_. Variants that were particularly good at duplication would automatically have come to predominate in the ancient organic soup. Varieties that did not duplicate, or that did so inaccurately, would have become relatively less numerous. This led to ever-increasing efficiency a
24、mong duplicating molecules.As the competition between duplicating molecules warmed up, success must have gone to the ones that happened to hit upon special tricks or devices for their own self-preservation and their own rapid replication. The rest of evolution may be regarded as a continuation of th
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