GWD13-36 Cannot differentiate btw A and C

xiao_zhutou

GWD-13-Q34 to GWD-13-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.

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

GWD-13-Q36:

The primary purpose of the passage is to

                        

A.   describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera

B.   present evidence that refutes a particular theory about the driving force behind population cycles in lepidoptera

present a hypothesis about the driving force behind population cycles in lepidoptera

describe the fluctuating patterns of population cycles in lepidoptera

question the idea that a single driving force is behind population cycles in lepidoptera

Answer is C. But is there anything wrong with A? To me, A and C are talking about the same thing... How do you eliminate A?

而今迈步从头越

The primary purpose of the passage is to                         

A.   describe the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera

C.  present a hypothesis about the driving force behind population cycles in lepidoptera

在没有看文章之前，我先纯粹的谈一下AC得差异（不涉及文章内容）：

A is focus on development of new techniques, C is focus on a hypothesis. The focus of A is different from that of C. And also the difference will determine the specific writing flowchart of the passage.

而今迈步从头越

After reading the passage, I vote the choice C.

P1 states several different variables that influence population levels and identifies the driving force.  At the end, it rules out other possibilities and asserts that the driving force is an agent rather than predatory birds or parasites.

the first sentence of P2 is the TS of the whole passage : Recent work suggests that this agent may be a virus. The rest of P2 describes the hypothesis and the new techniques made the hypothesis practical.

P3 states the attraction of virus hypothesis.

Choice A doesn't catch the focus of the passage--hypothesis. The information that the development of new techniques that may help to determine the driving force behind population cycles in lepidoptera is mentioned in the second paragraph but is not the focus of the passage.

xiao_zhutou

thanks for the prompt response!

deepinsorrow

Q34:

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

           

A.   New research reveals that the number of species of birds and parasites that prey on lepidoptera has dropped significantly in recent years.

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

C.   Recent experiments have revealed that the nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.

D.   Differences among the habitats of lepidoptera species make it difficult to assess the effects of weather on lepidoptera population cycles.

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

答案是B，可我选C，不知道为什么选B，也不知道为什么不选C。

从C来看， nuclear polyhedrosis virus is present in a number of predators and parasites of lepidoptera.不就可以说明这些virus是通过predators什么的传播到毛毛虫上的吗？然后就削弱了毛毛虫的数量不是通过 predators什么的来regulate了的吗？为什么不行呢？

B我当时都没看懂的说，请nn赐教

deepinsorrow

怎么没人回答我呢？我来顶一下。

是不是我的问题太小儿科了？

cdg2004

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.---support

B--栖息地的改变导致循环缩短。---假设循环周期为8-11年，根据B的意思栖息地的改变导致周期降到5年，---但折并不能解释栖息地的改变是产生这种循环的原因呀。

C---病毒存在于大量的捕食者中。---由于捕食者，导致病毒感染昆虫，产生人口循环。---weaken--I VOTE C.

Q37:

According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases

1. were not widely prevalent among insect populations generally


2. affected only the caterpillar life stage of lepidoptera


3. were the driving force behind lepidoptera population cycles


4. attacked already declining caterpillar populations


5. infected birds and parasites that prey on various species of lepidopte

Answer: D

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.  

I vote B.   but...had usually...it was underway rather than...initiated it. 其中，underway是否可以理解为B的life stage?

请NN指教。

[此贴子已经被作者于2005-6-17 17:32:59编辑过]

wangyu73cn

  but...had usually...it was underway rather than...initiated it. 其中，underway是否可以理解为B的life stage?

应该可以吧。

fchn951

答案BACD

yukon

真郁闷，回头一看都明白。当时就做不对。想发泄！