求教 GWD-TN-13 阅读一题

cherryfane

A small number of the forest species of lepidoptera (moths and butterflies,which exist as caterpillars during most of their life cycle) exhibit regularlyrecurring patterns of population growth and decline—such fluctuations inpopulation are known as population cycles. Although many different variables influence population levels, a regularpattern such as a population cycle seems to imply a dominant, drivingforce.  Identification of that drivingforce, however, has proved surprisingly elusive despite considerable research.The common approach of studying causes of population cycles by measuring the mortalitycaused by different agents, such as predatory birds or parasites, has beenunproductive in the case of lepidoptera. Moreover, population ecologists’ attempts to alter cycles by changingthe caterpillars’ habitat and by reducing caterpillar (25) populations have not succeeded. In short, the evidence impliesthat these insect populations, if not self-regulating, may at least beregulated by an agent more intimately connected with the insect than arepredatory birds or parasites. (30)  指出昆虫的数量是由于其它比捕食的鸟等联系更紧密的因素所影响的

Recent work suggests thatthis agent may be a virus.  For many years,viral disease had been reported in declining populations of caterpillars, but population ecologists had usually considered viral diseaseto have contributed to the decline once it was underway rather than to haveinitiated it. The recent work has been made possible by new techniquesof molecular biology that allow viral DNA to be detected at low concentrationsin the environment.  Nuclear polyhedrosisviruses are hypothesized to be the driving force behind population cycles in lepidopterain part because the viruses themselves follow an infectious cycle in which, ifprotected from direct sun light, they may remain virulent for many years in theenvironment, embedded in durable crystals of polyhedrin protein. Once ingestedby a caterpillar, the crystals dissolve, releasing the virus to infect theinsect’s cells. Late in the course of the infection, millions of new virusparticles are formed and enclosed in polyhedron crystals. These crystalsreenter the environment after the insect dies and decomposes, thus becomingavailable to infect other caterpillars.

     One of the attractions ofthis hypothesis is its broad applicability. Remarkably, despite significantdifferences in habitat and behavior, many species of lepidoptera havepopulation cycles of similar length, between eight and eleven years.  Nuclear polyhedrosis viral infection is onefactor these disparate species share.

34．Which of the following, if true, would most weaken theauthor’s conclusion in lines 25-30?

A.     !New research reveals that the number ofspecies of birds and parasites that prey on lepidoptera has droppedsignificantly in recent years.

     和捕猎的鸟的数量有关 weaken了呀？

B.      New experiments in which the habitats oflepidoptera are altered in previously untried ways result in the shortening oflepidoptera population cycles.  

   指出可能是栖息地这个因素影响了 不是support了作者观点吗？

C.     Recent experiments have revealed that thenuclear polyhedrosis virus is present in a number of predators and parasites oflepidoptera.

D.     Differences among the habitats of lepidopteraspecies make it difficult to assess the effects of weather on lepidopterapopulation cycles.

E.      Viral disease is typically observed in a largeproportion of the lepidoptera population.

我选了A 答案是B

求教个位NN 帮我看下！谢谢

5453

Moreover, population

            ecologists’ attempts to alter cycles

by changing the caterpillars’ habitat

and by reducing caterpillar popula-

(25)     tions have not succeeded.

说的是，科学家试图用改变caterpillar's habitat 来影响它们的cycle， 但是没有成功。也就是说，L虫的cycle 没有因此而改变。要想weaken, 就是象B所说的，新的实验采取以前没有试过的方法去改变L虫的居住所，结果L虫的cycle 变短了，证明cycle 是受habitat的影响的，即和科学家的推倒不同，所以weaken了。

A说L虫的天敌数目下降，没有提到cycle有没有受影响，所以无关。
http://forum.chasedream.com/GMAT_RC/thread-70665-1-1.html 2 楼解释