1、 目 录Passage 1.2Passage 2.4Passage 3.6Passage 4.8Passage 5.10Passage 6.12Passage 7.14Passage 8.17Passage 9.19Passage 10.21Passage 11.22Passage 12.24Passage 13.26Passage 14.27Passage 15.29Passage 16.31Passage 17.33Passage 18.36Passage 19.38Passage 20.40Passage 21.42Passage 22.45Passage 23.47Passage 24
2、.49Passage 25.50Passage 26.52Passage 27.54Passage 28.57Passage 29.59Passage 30.62Passage 31.64Passage 32.66Passage 33.69Passage 34.71Passage 35.72Passage 36.74Passage 37.76Passage 38.77Passage 39.78Passage 40.80Passage 41.82Passage 42.83Passage 43.84Passage 44.85Passage 45.86Passage 46.87Passage 47.
3、88Passage 48.90READING COMPREHENSIONPassage 1Caffeine, the stimulant in coffee, has been called“the most widely used psychoactive substance on Earth .”Synder, Daly and Bruns have recently proposed thatcaffeine affects behavior by countering the activity in(5) the human brain of a naturally occurring
4、 chemical calledadenosine. Adenosine normally depresses neuron firingin many areas of the brain. It apparently does this byinhibiting the release of neurotransmitters, chemicalsthat carry nerve impulses from one neuron to the next.(10) Like many other agents that affect neuron firing,adenosine must
5、first bind to specific receptors onneuronal membranes. There are at least two classesof these receptors, which have been designated A1 andA2. Snyder et al propose that caffeine, which is struc-(15) turally similar to adenosine, is able to bind to both typesof receptors, which prevents adenosine from
6、 attachingthere and allows the neurons to fire more readily thanthey otherwise would.For many years, caffeines effects have been attri-(20) buted to its inhibition of the production of phosphodi-esterase, an enzyme that breaks down the chemicalcalled cyclic AMP.A number of neurotransmitters exertthe
7、ir effects by first increasing cyclic AMP concentra-tions in target neurons. Therefore, prolonged periods at(25) the elevated concentrations, as might be brought aboutby a phosphodiesterase inhibitor, could lead to a greateramount of neuron firing and, consequently, to behav-ioral stimulation. But S
8、nyder et al point out that thecaffeine concentrations needed to inhibit the production(30) of phosphodiesterase in the brain are much higher thanthose that produce stimulation. Moreover, other com-pounds that block phosphodiesterases activity are notstimulants.To buttress their case that caffeine ac
9、ts instead by pre-(35) venting adenosine binding, Snyder et al compared thestimulatory effects of a series of caffeine derivatives withtheir ability to dislodge adenosine from its receptors inthe brains of mice. “In general,” they reported, “theability of the compounds to compete at the receptors(40
10、) correlates with their ability to stimulate locomotion inthe mouse; i.e., the higher their capacity to bind at thereceptors, the higher their ability to stimulate locomo-tion.” Theophylline, a close structural relative of caffeineand the major stimulant in tea, was one of the most(45) effective com
11、pounds in both regards.There were some apparent exceptions to the generalcorrelation observed between adenosine-receptor bindingand stimulation. One of these was a compound called3-isobuty1-1-methylxanthine(IBMX), which bound very(50) well but actually depressed mouse locomotion. Snyderet al suggest
12、 that this is not a major stumbling block totheir hypothesis. The problem is that the compound hasmixed effects in the brain, a not unusual occurrence withpsychoactive drugs. Even caffeine, which is generally(55) known only for its stimulatory effects, displays thisproperty, depressing mouse locomot
13、ion at very lowconcentrations and stimulating it at higher ones.1. The primary purpose of the passage is to(A) discuss a plan for investigation of a phenomenon that is not yet fully understood(B) present two explanations of a phenomenon and reconcile the differences between them(C) summarize two the
14、ories and suggest a third theory that overcomes the problems encountered in the first two(D) describe an alternative hypothesis and provide evidence and arguments that support it(E) challenge the validity of a theory by exposing the inconsistencies and contradictions in it2. According so Snyder et a
15、l, caffeine differs from adenosine in that caffeine(A) stimulates behavior in the mouse and in humans, whereas adenosine stimulates behavior in humans only(B) has mixed effects in the brain, whereas adenosine has only a stimulatory effect(C) increases cyclic AMP concentrations in target neurons, whe
16、reas adenosine decreases such concentrations(D) permits release of neurotransmitters when it is bound to adenosine receptors, whereas adenosine inhibits suchrelease(E) inhibits both neuron firing and the production of phosphodiesterase when there is a sufficient concentration inthe brain, whereas ad
17、enosine inhibits only neuron firing3. In response to experimental results concerning IBMX, Snyder et al contended that it is not uncommon forpsychoactive drugs to have(A) mixed effects in the brain(B) inhibitory effects on enzymes in the brain(C) close structural relationships with caffeine(D) depre
18、ssive effects on mouse locomotion(E) the ability to dislodge caffeine from receptors in the brain4. According to Snyder et al, all of the following compounds can bind to specific receptors in the brain EXCEPT(A) IBMX(B) caffeine(C) adenosine(D) theophylline(E) phosphodiesterase5. Snyder et al sugges
19、t that caffeines ability to bind to A1 and A2 receptors can be at least partially attributed towhich of the following?(A) The chemical relationship between caffeine and phosphodiesterase(B) The structural relationship between caffeine and adenosine(C) The structural similarity between caffeine and n
20、eurotransmitters(D) The ability of caffeine to stimulate behavior(E) The natural occurrence of caffeine and adenosine in the brain6. The author quotes Snyder et al in lines 38-43 most probably in order to(A) reveal some of the assumptions underlying their theory(B) summarize a major finding of their
21、 experiments(C) point out that their experiments were limited to the mouse(D) indicate that their experiments resulted only in general correlations(E) refute the objections made by supporters of the older theoryPassage 2Archaeology as a profession faces two major prob-lems. First, it is the poorest
22、of the poor. Only paltrysums are available for excavating and even less is avail-able for publishing the results and preserving the sites(5) once excavated. Yet archaeologists deal with pricelessobjects every day. Second, there is the problem of illegalexcavation, resulting in museum-quality pieces
23、beingsold to the highest bidder.I would like to make an outrageous suggestion that(10) would at one stroke provide funds for archaeology andreduce the amount of illegal digging. I would proposethat scientific archeological expeditions and govern-mental authorities sell excavated artifacts on the ope
24、nmarket. Such sales would provide substantial funds for(15) the excavation and preservation of archaeological sitesand the publication of results. At the same time, theywould break the illegal excavators grip on the market,thereby decreasing the inducement to engage in illegalactivities.(20) You mig
25、ht object that professionals excavate toacquire knowledge, not money. Moreover, ancient arti-facts are part of our global cultural heritage, whichshould be available for all to appreciate, not sold to thehighest bidder. I agree. Sell nothing that has unique(25) artistic merit or scientific value. Bu
26、t, you might reply,everything that comes our of the ground has scientificvalue. Here we part company. Theoretically, you may becorrect in claiming that every artifact has potential scien-tific value. Practically, you are wrong.(30) I refer to the thousands of pottery vessels and ancientlamps that ar
27、e essentially duplicates of one another. Inone small excavation in Cyprus, archaeologists recentlyuncovered 2,000 virtually indistinguishable small jugs ina single courtyard, Even precious royal seal impressions(35) known as/melekh handles have been found in abun-dance-more than 4,000 examples so fa
28、r.The basements of museums are simply not largeenough to store the artifacts that are likely to be discov-ered in the future. There is not enough money even to(40) catalogue the finds; as a result, they cannot be foundagain and become as inaccessible as if they had neverbeen discovered. Indeed, with
29、 the help of a computer,sold artifacts could be more accessible than are thepieces stored in bulging museum basements. Prior to(45) sale, each could be photographed and the list of thepurchasers could be maintained on the computer Apurchaser could even be required to agree to return thepiece if it s
30、hould become needed for scientific purposes.It would be unrealistic to suggest that illegal digging(50) would stop if artifacts were sold on the open market.But the demand for the clandestine product would besubstantially reduced. Who would want an unmarkedpot when another was available whose proven
31、ance wasknown, and that was dated stratigraphically by theprofessional archaeologist who excavated it?7. The primary purpose of the passage is to propose(A) an alternative to museum display of artifacts(B) a way to curb illegal digging while benefiting the archaeological profession(C) a way to distinguish artifacts with scie
