gre阅读练习每日一篇(三十四)

　　掌握了gre阅读里的长难句，到了实战演习的时候了。gre阅读练习每日一篇帮助gre考生循序渐进地进行练习和总结。希望gre考生在进行gre阅读练习时，也按着考试时候的时间规定自己的练习，这样才能有效果。

　　Jean Wagners most enduring contribution to the study of Afro-American poetry is his insistence that it be analyzed in a religious, as well as secular, frame of reference. The appropriateness of such an approach may seem self-evident for a tradition commencing with spirituals and owing its early forms, rhythms, vocabulary, and evangelical fervor to Wesleyan hymnals. But before Wagner a secular outlook that analyzed Black poetry solely within the context of political and social protest was dominant in the field.

　　It is Wagner who first demonstrated the essential fusion of racial and religious feeling in Afro-American poetry. The two, he argued, form a symbiotic union in which religious feelings are often applied to racial issues and racial problems are often projected onto a metaphysical plane. Wagner found this most eloquently illustrated in the Black spiritual, where the desire for freedom in this world and the hope for salvation in the next are inextricably intertwined.

　　17. The primary purpose of the passage is to

　　 contrast the theories of Jean Wagner with those of other contemporary critics

　　 document the influence of Jean Wagner on the development of Afro-American poetry

　　 explain the relevance of Jean Wagners work to the study of Afro-American religion

　　 indicate the importance of Jean Wagners analysis of Afro-American poetry

　　 present the contributions of Jean Wagner to the study of Black spirituals

　　18. All of the following aspects of Afro-American poetry are referred to in the passage as having been influenced by Wesleyan hymnals EXCEPT:

　　 subject matter

　　 word choice

　　 rhythm

　　 structure

　　 tone

　　19. It can be inferred from the passage that, before Wagner, most students of Afro-American poetry did which of the following?

　　 Contributed appreciably to the transfer of political protest from Afro-American poetry to direct political action.

　　 Ignored at least some of the historical roots of Afro-American poetry.

　　 Analyzed fully the aspects of social protest to be found in such traditional forms of Afro-American poetry as the Black spiritual.

　　 Regarded as unimportant the development of fervent emotionalism in a portion of Afro-American poetry.

　　 Concentrated on the complex relations between the technical elements in Afro-American poetry and its political content.

　　Two relatively recent independent developments stand behind the current major research effort on nitrogen fixation, the process by which bacteria symbiotically render leguminous plants independent of nitrogen fertilizer. The one development has been the rapid, sustained increase in the price of nitrogen fertilizer ). The other development has been the rapid growth of knowledge of and technical sophistication in genetic engineering. Fertilizer prices, largely tied to the price of natural gas, huge amounts of which go into the manufacture of fertilizer, will continue to represent an enormous and escalating economic burden on modern agriculture, spurring the search for alternatives to synthetic fertilizers. And genetic engineering is just the sort of fundamental breakthrough that opens up prospects of wholly novel alternatives. One such novel idea is that of inserting into the chromosomes of plants discrete genes that are not a part of the plants natural constitution: specifically, the idea of inserting into nonleguminous plants the genes, if they can be identified and isolated, that fit the leguminous plants to be hosts for nitrogen-fixing bacteria. Hence, the intensified research on legumes.

　　Nitrogen fixation is a process in which certain bacteria use atmospheric nitrogen gas, which green plants cannot directly utilize, to produce ammonia, a nitrogen compound plants can use. It is one of natures great ironies that the availability of nitrogen in the soil frequently sets an upper limit on plant growth even though the plants leaves are bathed in a sea of nitrogen gas. The leguminous plantsamong them crop plants such as soybeans, peas, alfalfa, and cloverhave solved the nitrogen supply problem by entering into a symbiotic relationship with the bacterial genus Rhizobium; as a matter of fact , there is a specific strain of Rhizobium for each species of legume. The host plant supplies the bacteria with food and a protected habitat and receives surplus ammonia in exchange. Hence, legumes can thrive in nitrogen-depleted soil.

　　Unfortunately, most of the major food cropsincluding maize, wheat, rice, and potatoescannot. On the contrary, many of the high-yielding hybrid varieties of these food crops bred during the Green Revolution of the 1960s were selected specifically to give high yields in response to generous applications of nitrogen fertilizer. This poses an additional, formidable challenge to plant geneticists: they must work on enhancing fixation within the existing symbioses. Unless they succeed, the yield gains of the Green Revolution will be largely lost even if the genes in legumes that equip those plants to enter into a symbiosis with nitrogen fixers are identified and isolated, and even if the transfer of those gene complexes, once they are found, becomes possible. The overall task looks forbidding, but the stakes are too high not to undertake it.

　　20. The primary purpose of the passage is to

　　 expose the fragile nature of the foundations on which the high yields of modern agriculture rest

　　 argue that genetic engineering promises to lead to even higher yields than are achievable with synthetic fertilizers

　　 argue that the capacity for nitrogen-fixing symbioses is transferable to nonleguminous plants

　　 explain the reasons for and the objectives of current research on nitrogen-fixing symbioses

　　 describe the nature of the genes that regulate the symbiosis between legumes and certain bacteria

　　21. According to the passage, there is currently no strain of Rhizobium that can enter into a symbiosis with

　　 alfalfa

　　 clover

　　 maize

　　 peas

　　 soybeans

　　22. The passage implies that which of the following is true of the bacterial genus Rhizobium?

　　 Rhizobium bacteria are found primarily in nitrogen-depleted soils.

　　 Some strains of Rhizobium are not capable of entering into a symbiosis with any plant.

　　 Newly bred varieties of legumes cannot be hosts to any strain of Rhizobium.

　　 Rhizobium bacteria cannot survive outside the protected habitat provided by host plants.

　　 Rhizobium bacteria produce some ammonia for their own purposes.

　　23. It can be inferred from the passage that which of the following was the most influential factor in bringing about intensified research on nitrogen fixation?

　　 The high yields of the Green Revolution

　　 The persistent upward surge in natural gas prices

　　 The variety of Rhizobium strains

　　 The mechanization of modern agriculture

　　 The environmental ill effects of synthetic fertilizers

　　24. Which of the following situations is most closely analogous to the situation described by the author as one of natures great ironies ?

　　 That of a farmer whose crops have failed because the normal midseason rains did not materialize and no preparations for irrigation had been made

　　 That of a long-distance runner who loses a marathon race because of a wrong turn that cost him twenty seconds

　　 That of shipwrecked sailors at sea in a lifeboat, with one flask of drinking water to share among them

　　 That of a motorist who runs out of gas a mere five miles from the nearest gas station

　　 That of travelers who want to reach their destination as fast and as cheaply as possible, but find that cost increases as travel speed increases

　　25. According to the passage, the ultimate goal of the current research on nitrogen fixation is to develop

　　 strains of Rhizobium that can enter into symbioses with existing varieties of wheat, rice, and other nonlegumes

　　 strains of Rhizobium that produce more ammonia for leguminous host plants than do any of the strains presently known

　　 varieties of wheat, rice, and other nonlegumes that yield as much as do existing varieties, but require less nitrogen

　　 varieties of wheat, rice, and other nonlegumes that maintain an adequate symbiotic relationship with nitrogen-fixing bacteria and produce high yields

　　 high-yielding varieties of wheat, rice, and other nonlegumes that are genetically equipped to fix nitrogen from the air without the aid of bacteria

　　26. The author regards the research program under discussion as

　　 original and extensive but ill-defined as to method

　　 necessary and ambitious but vulnerable to failure

　　 cogent and worthwhile but severely under-funded

　　 prohibitively expensive but conceptually elegant

　　 theoretically fascinating but practically useless

　　27. Most nearly parallel, in its fundamental approach, to the research program described in the passage would be a program designed to

　　 achieve greater frost resistance in frost-tender food plants by means of selective breeding, thereby expanding those plants area of cultivation

　　 achieve greater yields from food plants by interplanting crop plants that are mutually beneficial

　　 find inexpensive and abundant natural substances that could, without reducing yields, be substituted for expensive synthetic fertilizers

　　 change the genetic makeup of food plants that cannot live in water with high salinity, using genes from plants adapted to salt water

　　 develop, through genetic engineering, a genetic configuration for the major food plants that improves the storage characteristics of the edible portion of the plants

答案：17-27：DABDCEBCDBD