GRE阅读模拟在线练习附答案二百六十五

　　为了帮助大家高效备考GRE，新东方在线GRE频道为大家带来GRE阅读模拟在线练习附答案二百六十五，希望对大家GRE备考有所帮助。更多精彩尽请关注新东方在线GRE频道!

　　The defoliation of millions of acres of trees bymassive infestations of gypsy moth caterpillars is arecurring phenomenon in the northeastern UnitedStates.In studying these outbreaks, scientists havediscovered that affected trees fight back byreleasing toxic chemicals, mainly phenols, into theirfoliage. These noxious substances limit caterpillars'growth and reduce the number of eggs that femalemoths lay. Phenols also make the eggs smaller, which reduces the growth of the followingyear's caterpillars. Because the number of eggs a female moth produces is directly related toher size, and because her size is determined entirely by her feeding success as a caterpillar, the trees' defensive mechanism has an impact on moth fecundity. The gypsy moth is alsosubject to attack by the nucleopolyhedrosis virus, or wilt disease, a particularly important killerof the caterpillars in outbreak years. Caterpillars contract wilt disease when they eat a leaf towhich the virus, encased in a protein globule, has become attached. Once ingested by acaterpillar, the protein globule dissolves, releasing thousands of viruses, or virions, that afterabout two weeks multiply enough to fill the entire body cavity. When the caterpillar dies, thevirions are released to the outside, encased in a new protein globule synthesized from thecaterpillar's tissues and ready to be picked up by other caterpillars. Knowing that phenols, including tannins, often act by associating with and altering the activity of proteins, researchersfocused on the effects on caterpillars of ingesting the virus and leaves together. They foundthat on tannin-rich oak leaves, the virus is considerably less effective at killing caterpillarsthan when it is on aspen leaves, which are lower in phenols. In general, the moreconcentrated the phenols in tree leaves, the less deadly the virus. Thus, while highlyconcentrated phenols in tree leaves reduce the caterpillar population by limiting the size ofcaterpillars and consequently, the size of the female's egg cluster, these same chemicals alsohelp caterpillars survive by disabling the wilt virus. Forest stands of red oaks, with theirtannin-rich foliage, may even provide caterpillars with safe havens from disease. In standsdominated by trees such as aspen, however, incipient gypsy moth outbreaks are quicklysuppressed by viral epidemics.

　　Further research has shown that catefpillars become virtually immune to the wilt virus as thetrees on which they feed respond to increasing defoliation. The trees' own defenses raise thethreshold of caterpillar vulnerability to the disease, allowing populations to grow denserwithout becoming more susceptible to infection. For these reasons, the benefits to thecaterpillars of ingesting phenols appear to outweigh die costs. Given the presence of thevirus, the trees' defensive tactic apparently has backfired.

　　Which of the following statements best expresses the main point of the passage?

　　A.Recurring outbreaks of infestation by gypsy moth caterpillars have had a devastatingimpact on trees in the northeastern United States.

　　B.A mechanism used by trees to combat the threat from gypsy moth caterpillars hasactually made some trees more vulnerable to that threat.

　　C.Although deadly to gypsy moth caterpillars, wilt disease has failed to significantly affect thepopulation density of the caterpillars.

　　D.The tree species with the highest levels of phenols in their foliage are the most successful indefending themselves against gypsy moth caterpillars.

　　E.In their efforts to develop new methods for controlling gypsy moth caterpillars, researchershave focused on the effects of phenols in tree leaves on the insects'growth and reproduction.

　　In lines 12-14, the phrase “the trees'defensive mechanism has an impact on mothfecundity” refers to which of the following phenomena?

　　A.Female moths that ingest phenols are more susceptible to wilt virus, which causes them tolay smaller eggs.

　　B.Highly concentrated phenols in tree leaves limit caterpillars’ food supply, thereby reducingthe gypsy moth population.

　　C.Phenols attack the protein globule that protects moth egg clusters, making themvulnerable to wilt virus and lowering their survival rate.

　　D.Phenols in oak leaves drive gypsy moths into forest stands dominated by aspens, where theysuccumb to viral epidemics.

　　E.The consumption of phenols by caterpillars results in undersized female gypsy moths, whichtend to produce small egg clusters.

　　It can be inferred from the passage that wilt disease virions depend for their survivalon

　　A.protein synthesized from the tissues of a host caterpillar

　　B.aspen leaves with high concentrations of phenols

　　C.tannin-rich oak leaves

　　D.nutrients that they synthesize from gypsy moth egg clusters

　　E.a rising threshold of caterpillar vulnerability to wilt disease

　　Which of the following, if true, would most clearly demonstrate the operation of thetrees’ defensive mechanism as it is described in the first paragraph of the passage?

　　A.Caterpillars feeding on red oaks that were more than 50 percent defoliated grew to be onlytwo-thirds the size of those feeding on trees with relatively intact foliage.

　　B.Oak leaves in areas unaffected by gypsy moths were found to have higher levels of tanninon average than aspen leaves in areas infested with gypsy moths.

　　C.The survival rate of gypsy moth caterpillars exposed to the wilt virus was 40 percenthigher for those that fed on aspen leaves than for those that ate oak leaves.

　　D.Female gypsy moths produced an average of 25 percent fewer eggs in areas where the wiltvirus flourished than did moths in areas that were free of the virus.

　　E.Gypsy moth egg clusters deposited on oak trees were found to have relatively largeindividual eggs compared to those deposited on aspen trees.

　　Which of the following best describes the function of the third paragraph of thepassage?

　　A.It resolves a contradiction between the ideas presented in the first and second paragraphs.

　　B.It introduces research data to support the theory outlined in the second paragraph.

　　C.It draws a conclusion from conflicting evidence presented in the first two paragraphs.

　　D.It shows how phenomena described in the first and second paragraphs act in combination.

　　E.It elaborates on the thesis introduced in the first paragraph after a digression in the secondparagraph.

　　It can be inferred from the passage that gypsy moth caterpillars become immune tothe wilt virus as a result of

　　A.consuming a wide range of nutrients from a variety of leaf types

　　B.feeding on leaves that contain high levels of phenols

　　C.producing fewer offspring, which favors the survival of the hardiest individuals

　　D.ingesting the virus together with leaves that do not contain tannin

　　E.growing population density, which outstrips the ability of the virus to multiply and spread

　　Which of the following statements about gypsy moth caterpillars is supported byinformation presented in the passage?

　　A.Wilt disease is more likely to strike small gypsy moth caterpillars than large ones.

　　B.The concentration of phenols in tree leaves increases as the gypsy moth caterpillarpopulation dies off.

　　C.Female gypsy moth caterpillars stop growing after they ingest leaves containing phenols.

　　D.Differing concentrations of phenols in leaves have differing effects on the ability of the wiltvirus to kill gypsy moth caterpillars.

　　E.The longer a gypsy moth population is exposed to wilt disease, the greater the likelihoodthat the gypsy moth caterpillars will become immune to the virus.

　　正确答案:B E A A D B D

　　以上就是关于“GRE阅读模拟在线练习附答案二百六十五”的内容，更多精彩内容，请关注GRE频道!