GWD13-34 亟待解决的一个问题

greatvampire

      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.

--------------------------------------------------------------------------------

Q34:

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

                        

1. New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.
   
2. New experiments in which the habitats of lepidoptera are altered in previously untried ways result in the shortening of lepidoptera population cycles.
   
3. Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.
   
4. Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.
   
5. Viral disease is typically observed in a large proportion of the lepidoptera population

同天山5

fair_sword 说曾做过详细的解答，可我始终没找到贴子
见http://forum.chasedream.com/dispbbs.asp?BoardID=25&ID=62051

携隐认为：

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)

见http://forum.chasedream.com/dispbbs.asp?BoardID=25&ID=70665

我第一次做天山5选的C，后来改成了B。现在回过头来做GWD13的时候又选了C。
仔细看了以后还是觉得选C好。关键在于题中提出的是the author’s conclusion in lines 25-30，既然是这样，就没有理由是25行的前半句。
而应该是

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.

而且这里的C也能够weaken“不是鸟或者寄生虫而是更可能昆虫”的观点。既然这种virus也出现在a number of predators and parasites of lepidoptera的身上，就可以证明虫被它们捕食了。

greatvampire

up up

请大家帮帮忙~

dphxmg

介绍一个自然现象，引入一个解释，然后驳斥该解释，再引入一个新的解释，并且给出了新解释的技术基础和mechanism, 最后给出新解释的优点。

greatvampire

dphxmg的解释很模糊啊

就这题而言 觉得哪个更好呢