gwd13-34

Q34 to Q37:

      A small number of the forest

             species of lepidoptera (moths and

             butterflies, which exist as caterpillars

Line     during most of their life cycle) exhibit

  (5)      regularly recurring patterns of popu-

lation growth and decline—such

fluctuations in population are known

as population cycles.  Although many

different variables influence popula-

(10)     tion levels, a regular pattern such as

a population cycle seems to imply a

dominant, driving force.  Identification

of that driving force, however, has

proved surprisingly elusive despite

(15)     considerable research.  The com-

mon approach of studying causes of

population cycles by measuring the

mortality caused by different agents,

such as predatory birds or parasites,

(20)     has been unproductive in the case of

             lepidoptera.  Moreover, population

             ecologists’ attempts to alter cycles

by changing the caterpillars’ habitat

and by reducing caterpillar popula-

(25)     tions have not succeeded.  In short,

the evidence implies that these insect

populations, if not self-regulating, may

at least be regulated by an agent more

intimately connected with the insect than

(30)     are predatory birds or parasites.

      Recent work suggests that this

agent may be a virus.  For many

             years, viral disease had been

reported in declining populations

(35)   of caterpillars, but population ecolo-

gists had usually considered viral

disease to have contributed to the

decline once it was underway rather

than to have initiated it.  The recent

(40)    work has been made possible by

new techniques of molecular biology

that allow viral DNA to be detected

at low concentrations in the environ-

ment.  Nuclear polyhedrosis viruses

(45)     are hypothesized to be the driving

force behind population cycles in

lepidoptera in part because the

viruses themselves follow an infec-

tious cycle in which, if protected from

(50)     direct sun light, they may remain

virulent for many years in the envi-

ronment, embedded in durable

crystals of polyhedrin protein.

Once ingested by a caterpillar,

(55)     the crystals dissolve, releasing

the virus to infect the insect’s cells.

Late in the course of the infection,

millions of new virus particles are

formed and enclosed in polyhedrin

(60)     crystals.  These crystals reenter the

environment after the insect dies and

decomposes, thus becoming avail-

able to infect other caterpillars.

      One of the attractions of this

(65)     hypothesis is its broad applicability.

Remarkably, despite significant differ-

ences in habitat and behavior, many

species of lepidoptera have population

cycles of similar length, between eight

(70)     and eleven years.  Nuclear polyhe-

drosis viral infection is one factor these

disparate species share.

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Q34:

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

我也选了A, 原文结论说不是由鸟或parasites造成的. 要求削弱. A说鸟和寄生虫的数量大幅下降,说明还是有可能由鸟和parasites造成的嘛. B说改了地方就下降了,说明是地方造成的,不是鸟和寄生虫造成的,这不是加强了原文的结论嘛.

如果答案一定是B,那只能理解为在阅读中削弱题要求削弱的就是结论的上一句话

牛牛们请指教!!

携隐，

我开始作题的时候选C，是因为没有看清楚B的含义。后来我发现还是B 对。请看

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。

这个到25行就结束了,我原来选A是因为题目问的是25-30.原文是:

In short,

the evidence implies that these insect

populations, if not self-regulating, may

at least be regulated by an agent more

intimately connected with the insect than

(30)     are predatory birds or parasites.

这个结论是说: 虫虫的数量周期一定是被跟虫虫自己本身密切相关的(这个是核心句), 而不是鸟或寄生虫(这个是than后的附属内容)

我当时理解结论为: 不是鸟和寄生虫导致改变.然后削弱就是要削弱: 就是鸟导致它们改变. 所以就选了A. 现在看看,结论不是后面那个附属,是前面这个"跟自身相关". B正好说明不是跟自身相关而是跟环境有关的.

发现现在ETS出的选项都有这样的趋势, 如果要求定位哪一句, 结论肯定在跟这句并列的另一个理由中.

D是无关选项啊

B

原选A   还是自己理解有问题，，题目是 这些证据表明===〉削弱  证据没有表明  ====〉B  与鸟和寄生物无关  ---------只能说做阅读要小心啊。。。。