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18. GWD- 毛毛虫的生命长度
By williams（680 50，31）T-9-Q20-Q23：GWD-13-34~37
43. GWD-13-Q34 -Q37是谁控制着毛毛虫的生命长度
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.老观点及其方法
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.新观点及其论据
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.
题目基本相同，可能有变体
T-9-20:GWD-13-34:
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.
--------------------------------------------------------------------
T-9-21:GWD-13-35:
It can be inferred from the passage that the mortality caused by agents such as predatory birds or parasites was measured in an attempt to
A. develop an explanation for the existence of lepidoptera population cycles
B. identify behavioral factors in lepidoptera that affect survival rates
C. identify possible methods for controlling lepidoptera population growth
D. provide evidence that lepidoptera populations are self-regulating
E. determine the life stages of lepidoptera at which mortality rates are highest
--------------------------------------------------------------------
T-9-22:GWD-13-36:
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
C. present a hypothesis about the driving force behind population cycles in Lepidoptera
D. describe the fluctuating patterns of population cycles in Lepidoptera
E. question the idea that a single driving force is behind population cycles in Lepidoptera
--------------------------------------------------------------------
T-9-23:GWD-13-37:
According to the passage, before the discovery of new techniques for detecting viral DNA, population ecologists believed that viral diseases
A. were not widely prevalent among insect populations generally
B. affected only the caterpillar life stage of lepidoptera
C. were the driving force behind lepidoptera population cycles
D. attacked already declining caterpillar populations
E. infected birds and parasites that prey on various species of Lepidoptera
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发表于 2010-6-16 12:06:56
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