GRE阅读练习每日一篇(三十八)

　　编辑点评： GRE阅读的方法相信大家已经积累了很多了，本文就为大家提供一些GRE阅读的材料，大家来练一练，把平时学到的东西运用到实际中，也多多积累词汇和句子，提高自己的阅读能力。

　　每天做一些标准的GRE阅读练习，有助于大家在GRE考试的复习过程中不断地进行练习和总结。希望大家在进行GRE阅读练习时，充分运用平时所积累的知识，这样才能有效果。

　　Traditional research has confronted only Mexican and United States interpretations of Mexican-American culture. Now we must also examine the culture as we Mexican Americans have experienced it, passing from a sovereign people to compatriots with newly arriving settlers to, finally, a conquered people a charter minority on our own land.

　　When the Spanish first came to Mexico, they intermarried with and absorbed the culture of the indigenous Indians. This policy of colonization through acculturation was continued when Mexico acquired Texas in the early 1800 s and brought the indigenous Indians into Mexican life and government. In the 1820 s, United States citizens migrated to Texas, attracted by land suitable for cotton. As their numbers became more substantial, their policy of acquiring land by subduing native populations began to dominate. The two ideologies clashed repeatedly, culminating in a military conflict that led to victory for the United States. Thus, suddenly deprived of our parent culture, we had to evolve uniquely Mexican-American modes of thought and action in order to survive.

　　17. The author s purpose in writing this passage is primarily to

　　suggest the motives behind Mexican and United States intervention in Texas

　　document certain early objectives of Mexican-American society

　　provide a historical perspective for a new analysis of Mexican-American culture

　　appeal to both Mexican and United States scholars to give greater consideration to economic interpretations of history

　　bring to light previously overlooked research on Mexican Americans

　　18. The author most probably uses the phrase charter minority to reinforce the idea that Mexican Americans

　　are a native rather than an immigrant group in the United States

　　played an active political role when Texas first became part of the United States

　　recognized very early in the nineteenth century the need for official confirmation of their rights of citizenship

　　have been misunderstood by scholars trying to interpret their culture

　　identify more closely with their Indian heritage than with their Spanish heritage

　　19. According to the passage, a major difference between the colonization policy of the United States and that of Mexico in Texas in the 1800 s was the

　　degree to which policies were based on tradition

　　form of economic interdependency between different cultural groups

　　number of people who came to settle new areas

　　treatment of the native inhabitants

　　relationship between the military and the settlers

　　20. Which of the following statements most clearly contradicts the information in this passage?

　　In the early 1800 s, the Spanish committed more resources to settling California than to developing Texas.

　　While Texas was under Mexican control, the population of Texas quadrupled, in spite of the fact that Mexico discouraged immigration from the United States.

　　By the time Mexico acquired Texas, many Indians had already married people of Spanish heritage.

　　Many Mexicans living in Texas returned to Mexico after Texas was annexed by the United States.

　　Most Indians living in Texas resisted Spanish acculturation and were either killed or enslaved.

　　This passage was adapted from an article published in 1982.

　　Until about five years ago, the very idea that peptide hormones might be made anywhere in the brain besides the hypothalamus was astounding. Peptide hormones, scientists thought, were made by endocrine glands and the hypothalamus was thought to be the brains only endocrine gland. What is more, because peptide hormones cannot cross the blood-brain barrier, researchers believed that they never got to any part of the brain other than the hypothalamus, where they were simply produced and then released into the bloodstream.

　　But these beliefs about peptide hormones were questioned as laboratory after laboratory found that antiserums to peptide hormones, when injected into the brain, bind in places other than the hypothalamus, indicating that either the hormones or substances that cross-react with the antiserums are present. The immunological method of detecting peptide hormones by means of antiserums, however, is imprecise. Cross-reactions are possible and this method cannot determine whether the substances detected by the antiserums really are the hormones, or merely close relatives. Furthermore, this method cannot be used to determine the location in the body where the detected substances are actually produced.

　　New techniques of molecular biology, however, provide a way to answer these questions. It is possible to make specific complementary DNA s that can serve as molecular probes to seek out the messenger RNA s of the peptide hormones. If brain cells are making the hormones, the cells will contain these mRNA s. If the products the brain cells make resemble the hormones but are not identical to them, then the cDNA s should still bind to these mRNA s, but should not bind as tightly as they would to mRNA s for the true hormones. The cells containing these mRNA s can then be isolated and their mRNA s decoded to determine just what their protein products are and how closely the products resemble the true peptide hormones.

　　The molecular approach to detecting peptide hormones using cDNA probes should also be much faster than the immunological method because it can take years of tedious purifications to isolate peptide hormones and then develop antiserums to them. Roberts, expressing the sentiment of many researchers, states: I was trained as an endocrinologist. But it became clear to me that the field of endocrinology needed molecular biology input. The process of grinding out protein purifications is just too slow.

　　If, as the initial tests with cDNA probes suggest, peptide hormones really are made in the brain in areas other than the hypothalamus, a theory must be developed that explains their function in the brain. Some have suggested that the hormones are all growth regulators, but Rosen s work on rat brains indicates that this cannot be true. A number of other researchers propose that they might be used for intercellular communication in the brain.

　　21. Which of the following titles best summarizes the passage?

　　Is Molecular Biology the Key to Understanding Intercellular Communication in the Brain?

　　Molecular Biology: Can Researchers Exploit Its Techniques to Synthesize Peptide Hormones?

　　The Advantages and Disadvantages of the Immunological Approach to Detecting Peptide Hormones

　　Peptide Hormones: How Scientists Are Attempting to Solve Problems of Their Detection and to Understand Their Function

　　Peptide Hormones: The Role Played by Messenger RNA s in Their Detection

　　22. The passage suggests that a substance detected in the brain by use of antiserums to peptide hormones may

　　have been stored in the brain for a long period of time

　　play no role in the functioning of the brain

　　have been produced in some part of the body other than the brain

　　have escaped detection by molecular methods

　　play an important role in the functioning of the hypothalamus

　　23. According to the passage, confirmation of the belief that peptide hormones are made in the brain in areas other than the hypothalamus would force scientists to

　　reject the theory that peptide hormones are made by endocrine glands

　　revise their beliefs about the ability of antiserums to detect peptide hormones

　　invent techniques that would allow them to locate accurately brain cells that produce peptide hormones

　　search for techniques that would enable them to distinguish peptide hormones from their close relatives

　　develop a theory that explains the role played by peptide hormones in the brain

　　24. Which of the following is mentioned in the passage as a drawback of the immunological method of detecting peptide hormones?

　　It cannot be used to detect the presence of growth regulators in the brain.

　　It cannot distinguish between the peptide hormones and substances that are very similar to them.

　　It uses antiserums that are unable to cross the blood-brain barrier.

　　It involves a purification process that requires extensive training in endocrinology.

　　It involves injecting foreign substances directly into the bloodstream.

　　25. The passage implies that, in doing research on rat brains, Rosen discovered that

　　peptide hormones are used for intercellular communication

　　complementary DNA s do not bind to cells producing peptide hormones

　　products closely resembling peptide hormones are not identical to peptide hormones

　　some peptide hormones do not function as growth regulators

　　antiserums cross-react with substances that are not peptide hormones

　　26. Which of the following is a way in which the immunological method of detecting peptide hormones differs from the molecular method?

　　The immunological method uses substances that react with products of hormone-producing cells, whereas the molecular method uses substances that react with a specific component of the cells themselves.

　　The immunological method has produced results consistent with long-held beliefs about peptide hormones, whereas the molecular method has produced results that upset these beliefs.

　　The immunological method requires a great deal of expertise, whereas the molecular method has been used successfully by nonspecialists.

　　The immunological method can only be used to test for the presence of peptide hormones within the hypothalamus, whereas the molecular method can be used throughout the brain.

　　The immunological method uses probes that can only bind with peptide hormones, whereas the molecular method uses probes that bind with peptide hormones and substances similar to them.

　　27. The idea that the field of endocrinology can gain from developments in molecular biology is regarded by Roberts with

　　incredulity

　　derision

　　indifference

　　pride

　　enthusiasm

　　答案：17-27：CADEDCEBDAE