gre阅读练习每日一篇(五十)

　　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。

　　For some time scientists have believed that cholesterol plays a major role in heart disease because people with familial hypercholesterolemia , a genetic defect, have six to eight times the normal level of cholesterol in their blood and they invariably develop heart disease. These people lack cell-surface receptors for low-density lipoproteins , which are the fundamental carriers of blood cholesterol to the body cells that use cholesterol. Without an adequate number of cell-surface receptors to remove LDLs from the blood, the cholesterol-carrying LDLs remain in the blood, increasing blood cholesterol levels. Scientists also noticed that people with familial hypercholesterolemia appear to produce more LDLs than normal individuals. How, scientists wondered, could a genetic mutation that causes a slowdown in the removal of LDLs from the blood also result in an increase in the synthesis of this cholesterol-carrying protein?

　　Since scientists could not experiment on human body tissue, their knowledge of familial hypercholesterolemia was severely limited. However, a breakthrough came in the laboratories of Yoshio Watanabe of Kobe University in Japan in 1980. Watanabe noticed that a male rabbit in his colony had ten times the normal concentration of cholesterol in its blood. By appropriate breeding, Watanabe obtained a strain of rabbits that had very high cholesterol levels. These rabbits spontaneously developed heart disease. To his surprise, Watanabe further found that the rabbits, like humans with familial hypercholesterolemia, lacked LDL receptors. Thus, scientists could study these Watanabe rabbits to gain a better understanding of familial hypercholesterolemia in humans.

　　Prior to the breakthrough at Kobe University, it was known that LDLs are secreted from the liver in the form of a precursor, called very low-density lipoproteins , which carry triglycerides as well as relatively small amounts of cholesterol. The triglycerides are removed from the VLDLs by fatty and other tissues. What remains is a remnant particle that must be removed from the blood. What scientists learned by studying the Watanabe rabbits is that the removal of the VLDL remnant requires the LDL receptor. Normally, the majority of the VLDL remnants go to the liver where they bind to LDL receptors and are degraded. In the Watanabe rabbit, due to a lack of LDL receptors on liver cells, the VLDL remnants remain in the blood and are eventually converted to LDLs. The LDL receptors thus have a dual effect in controlling LDL levels. They are necessary to prevent oversynthesis of LDLs from VLDL remnants and they are necessary for the normal removal of LDLs from the blood. With this knowledge, scientists are now well on the way toward developing drugs that dramatically lower cholesterol levels in people afflicted with certain forms of familial hypercholesterolemia.

　　17. In the passage, the author is primarily concerned with

　　 presenting a hypothesis and describing compelling evidence in support of it

　　 raising a question and describing an important discovery that led to an answer

　　 showing that a certain genetically caused disease can be treated effectively with drugs

　　 explaining what causes the genetic mutation that leads to heart disease

　　 discussing the importance of research on animals for the study of human disease

　　18. Which of the following drugs, if developed, would most likely be an example of the kind of drug mentioned in line 53?

　　 A drug that stimulates the production of VLDL remnants

　　 A drug that stimulates the production of LDL receptors on the liver

　　 A drug that stimulates the production of an enzyme needed for cholesterol production

　　 A drug that suppresses the production of body cells that use cholesterol

　　 A drug that prevents triglycerides from attaching to VLDLs

　　19. The passage supplies information to answer which of the following questions?

　　 Which body cells are the primary users of cholesterol?

　　 How did scientists discover that LDLs are secreted from the liver in the form of a precursor?

　　 Where in the body are VLDL remnants degraded?

　　 Which body tissues produce triglycerides?

　　 What techniques are used to determine the presence or absence of cell-surface receptors?

　　20. According to the passage, by studying the Watanabe rabbits scientists learned that

　　 VLDL remnants are removed from the blood by LDL receptors in the liver

　　 LDLs are secreted from the liver in the form of precursors called VLDLs

　　 VLDL remnant particles contain small amounts of cholesterol

　　 triglycerides are removed from VLDLs by fatty tissues

　　 LDL receptors remove LDLs from the blood

　　21. The development of drug treatments for some forms of familial hypercholesterolemia is regarded by the author as

　　 possible, but not very important

　　 interesting, but too costly to be practical

　　 promising, but many years off

　　 extremely unlikely

　　 highly probable

　　22. The passage implies that if the Watanabe rabbits had had as many LDL receptors on their livers as do normal rabbits, the Watanabe rabbits would have been

　　 less likely than normal rabbits to develop heart disease

　　 less likely than normal rabbits to develop high concentrations of cholesterol in their blood

　　 less useful than they actually were to scientists in the study of familial hypercholesterolemia in humans

　　 unable to secrete VLDLs from their livers

　　 immune to drugs that lower cholesterol levels in people with certain forms of familial hypercholesterolemia

　　23. The passage implies that Watanabe rabbits differ from normal rabbits in which of the following ways?

　　 Watanabe rabbits have more LDL receptors than do normal rabbits.

　　 The blood of Watanabe rabbits contains more VLDL remnants than does the blood of normal rabbits.

　　 Watanabe rabbits have fewer fatty tissues than do normal rabbits.

　　 Watanabe rabbits secrete lower levels of VLDLs than do normal rabbits.

　　 The blood of Watanabe rabbits contains fewer LDLs than does the blood of normal rabbits.

　　When speaking of Romare Bearden, one is tempted to say, A great Black American artist. The subject matter of Beardens collages is certainly Black. Portrayals of the folk of Mecklenburg County, North Carolina, whom he remembers from early childhood, of the jazz musicians and tenement roofs of his Harlem days, of Pittsburgh steelworkers, and his reconstruction of classical Greek myths in the guise of the ancient Black kingdom of Benin, attest to this. In natural harmony with this choice of subject matter are the social sensibilities of the artist, who remains active today with the Cinque Gallery in Manhattan, which he helped found and which is devoted to showing the work of minority artists.

　　Then why not call Bearden a Black American artist? Because ultimately this categorization is too narrow. What stands up in the end is structure, Bearden says. What I try to do is amplify. If I were just creating a picture of a farm woman from back home, it would have meaning to her and people there. But art amplifies itself to something universal.

　　24. According to the passage, all of the following are depicted in Beardens collages EXCEPT:

　　 workers in Pittsburghs steel mills

　　 scenes set in the ancient kingdom of Benin

　　 people Bearden knew as a child

　　 traditional representations of the classical heroes of Greek mythology

　　 the jazz musicians of the Harlem Bearden used to know

　　25. The author suggests that Bearden should not be called a Black American artist because

　　 there are many collages by Bearden in which the subject matter is not Black

　　 Beardens work reflects the Black American experience in a highly individual style

　　 through the structure of Beardens art his Black subjects come to represent all of humankind

　　 Beardens true significance lies not so much in his own work as in his efforts to help other minority artists

　　 much of Beardens work uses the ancient Black kingdom of Benin for its setting

　　26. Beardens social sensibilities and the subject matter of his collages are mentioned by the author in order to explain

　　 why one might be tempted to call Bearden a Black American artist

　　 why Bearden cannot be readily categorized

　　 why Beardens appeal is thought by many to be ultimately universal

　　 how deeply an artists artistic creations are influenced by he artists social conscience

　　 what makes Bearden unique among contemporary Black American artists

　　27. The author of the passage is chiefly concerned with

　　 discussing Beardens philosophy of art

　　 assessing the significance of the ethnic element in Beardens work

　　 acknowledging Beardens success in giving artistic expression to the Black American experience

　　 pointing out Beardens helpfulness to other minority artists

　　 tracing Beardens progress toward artistic maturity

　　答案：17-27：BBCAECBDCAB