纵深留学考试 缔造高分传奇
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托福最新阅读模拟试题——出国留学
内容
财务内部控制制度的内容财务内部控制制度的内容人员招聘与配置的内容项目成本控制的内容消防安全演练内容
摘要:托福阅读高分的关键是在于多看多练,同学们在日常练习中应该
重视托福阅读材料的分析。前程百利为大家整理提供托福阅读练习,供各位考生复习
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托福阅读模拟试题之生态系统的长期稳定。
The Long-Term Stability of Ecosystems
Plant communities assemble themselves flexibly, and their particular
structure depends on the specific history of the area. Ecologists use the term
“succession” to refer to the changes that happen in plant communities and
ecosystems over time. The first community in a succession is called a pioneer
community, while the long-lived community at the end of succession is called
a climax community. Pioneer and successional plant communities are said to
change over periods from 1 to 500 years. These changes—in plant numbers and
the mix of species—are cumulative. Climax communities themselves change but
over periods of time greater than about 500 years.
An ecologist who studies a pond today may well find it relatively
纵深留学考试 缔造高分传奇
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unchanged in a year’s time. Individual fish may be replaced, but the number
of fish will tend to be the same from one year to the next. We can say that
the properties of an ecosystem are more stable than the individual organisms
that compose the ecosystem.
At one time, ecologists believed that species diversity made ecosystems
stable. They believed that the greater the diversity the more stable the
ecosystem. Support for this idea came from the observation that long-lasting
climax communities usually have more complex food webs and more species
diversity than pioneer communities. Ecologists concluded that the apparent
stability of climax ecosystems depended on their complexity. To take an extreme
example, farmlands dominated by a single crop are so unstable that one year
of bad weather or the invasion of a single pest can destroy the entire crop.
In contrast, a complex climax community, such as a temperate forest, will
tolerate considerable damage from weather to pests.
The question of ecosystem stability is complicated, however. The first
problem is that ecologists do not all agree what “stability” means. Stability
can be defined as simply lack of change. In that case, the climax community
would be considered the most stable, since, by definition, it changes the least
over time. Alternatively, stability can be defined as the speed with which an
纵深留学考试 缔造高分传奇
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ecosystem returns to a particular form following a major disturbance, such as
a fire. This kind of stability is also called resilience. In that case, climax
communities would be the most fragile and the least stable, since they can
require hundreds of years to return to the climax state.
Even the kind of stability defined as simple lack of change is not always
associated with maximum diversity. At least in temperate zones, maximum
diversity is often found in mid-successional stages, not in the climax
community. Once a redwood forest matures, for example, the kinds of species
and the number of individuals growing on the forest floor are reduced. In
general, diversity, by itself, does not ensure stability. Mathematical models
of ecosystems likewise suggest that diversity does not guarantee ecosystem
stability—just the opposite, in fact. A more complicated system is, in general,
more likely than a simple system to break down. A fifteen-speed racing bicycle
is more likely to break down than a child’s tricycle.
Ecologists are especially interested to know what factors contribute
to the resilience of communities because climax communities all over the world
are being severely damaged or destroyed by human activities. The destruction
caused by the volcanic explosion of Mount St. Helens, in the northwestern United
States, for example, pales in comparison to the destruction caused by humans.
纵深留学考试 缔造高分传奇
地址:北京市海淀区海淀北二街 8 号 中关村 SOHO A 区 2 层
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We need to know what aspects of a community are most important to the
community’s resistance to destruction, as well as its recovery.
Many ecologists now think that the relative long-term stability of
climax communities comes not from diversity but from the “patchiness” of the
environment, an environment that varies from place to place supports more kinds
of organisms than an environment that is uniform. A local population that goes
extinct is quickly replaced by immigrants from an adjacent community. Even if
the new population is of a different species, it can approximately fill the
niche vacated by the extinct population and keep the food web intact.
Paragraph 1: Plant communities assemble themselves flexibly, and their
particular structure depends on the specific history of the area. Ecologists
use the term “succession” to refer to the changes that happen in plant
communities and ecosystems over time. The first community in a succession is
called a pioneer community, while the long-lived community at the end of
succession is called a climax community. Pioneer and successional plant
communities are said to change over periods from 1 to 500 years. These
changes—in plant numbers and the mix of species—are cumulative. Climax
communities themselves change but over periods of time greater than about 500
years.
纵深留学考试 缔造高分传奇
地址:北京市海淀区海淀北二街 8 号 中关村 SOHO A 区 2 层
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1. The word “particular” in the passage is closest in meaning to
○Natural
○Final
○Specific
○Complex
2. According to paragraph 1, which of the following is NOT true of climax
communities?
○They occur at the end of a succession.
○They last longer than any other type of community.
○The numbers of plants in them and the mix of species do not change.
○They remain stable for at least 500 years at a time.
Paragraph 2: An ecologist who studies a pond today may well find it
relatively unchanged in a year’s time. Individual fish may be replaced, but
the number of fish will tend to be the same from one year to the next. We can
say that the properties of an ecosystem are more stable than the individual
organisms that compose the ecosystem.
3. According to paragraph 2, which of the following principles of
纵深留学考试 缔造高分传奇
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ecosystems can be learned by studying a pond?
○Ecosystem properties change more slowly than individuals in the
system.
○The stability of an ecosystem tends to change as individuals are
replaced.
○Individual organisms are stable from one year to the next.
○A change in the members of an organism does not affect an ecosystem’s
properties
Paragraph 3: At one time, ecologists believed that species diversity
made ecosystems stable. They believed that the greater the diversity the more
stable the ecosystem. Support for this idea came from the observation that
long-lasting climax communities usually have more complex food webs and more
species diversity than pioneer communities. Ecologists concluded that the
apparent stability of climax ecosystems depended on their complexity. To take
an extreme example, farmlands dominated by a single crop are so unstable that
one year of bad weather or the invasion of a single pest can destroy the entire
crop. In contrast, a complex climax community, such as a temperate forest, will
tolerate considerable damage from weather of pests.
4. According to paragraph 3, ecologists once believed that which of
纵深留学考试 缔造高分传奇
地址:北京市海淀区海淀北二街 8 号 中关村 SOHO A 区 2 层
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the following illustrated the most stable ecosystems?
○Pioneer communities
○Climax communities
○Single-crop farmlands
○Successional plant communities
Paragraph 4: The question of ecosystem stability is complicated,
however. The first problem is that ecologists do not all agree what
“stability” means. Stability can be defined as simply lack of change. In that
case, the climax community would be considered the most stable, since, by
definition, it changes the least over time. Alternatively, stability can be
defined as the speed with which an ecosystem returns to a particular form
following a major disturbance, such as a fire. This kind of stability is also
called resilience. In that case, climax communities would be the most fragile
and the least stable, since they can require hundreds of years to return to
the climax state.
5. According to paragraph 4, why is the question of ecosystem stability
complicated?
○The reasons for ecosystem change are not always clear.
○Ecologists often confuse the word “stability” with the word
纵深留学考试 缔造高分传奇
地址:北京市海淀区海淀北二街 8 号 中关村 SOHO A 区 2 层
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“resilience.”
○The exact meaning of the word “stability” is debated by ecologists.
○There are many different answers to ecological questions.
6. According to paragraph 4, which of the following is true of climax
communities?
○They are more resilient than pioneer communities.
○They can be considered both the most and the least stable communities.
○They are stable because they recover quickly after major
disturbances.
○They are the most resilient communities because they change the least
over time.
Paragraph 5: Even the kind of stability defined as simple lack of change
is not always associated with maximum diversity. At least in temperate zones,
maximum diversity is often found in mid-successional stages, not in the climax
community. Once a redwood forest matures, for example, the kinds of species
and the number of individuals growing on the forest floor are reduced. In
general, diversity, by itself, does not ensure stability. Mathematical models
of ecosystems likewise suggest that diversity does not guarantee ecosystem
stability—just the opposite, in fact. A more complicated system is, in general,
纵深留学考试 缔造高分传奇
地址:北京市海淀区海淀北二街 8 号 中关村 SOHO A 区 2 层
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more likely than a simple system to break down. (A fifteen-speed racing bicycle
is more likely to break down than a child’s tricycle.)
7. Which of the following can be inferred from paragraph 5 about redwood
forests?
○They become less stable as they mature.
○They support many species when they reach climax.
○They are found in temperate zones.
○They have reduced diversity during mid-successional stages.
8. The word “guarantee” in the passage is closest in meaning to
○Increase
○Ensure
○Favor
○Complicate
9. In paragraph 5, why does the author provide the information that
“(A fifteen-speed racing bicycle is more likely to break down than a child’s
tricycle)”?
○To illustrate a general principle about the stability of systems by
using an everyday example
纵深留学考试 缔造高分传奇
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○To demonstrate that an understanding of stability in ecosystems can
be applied to help understand stability in other situations
○To make a comparison that supports the claim that, in general,
stability increases with diversity
○To provide an example that contradicts mathematical models of
ecosystems
Paragraph 6: Ecologists are especially interested to know what factors
contribute to the resilience of communities because climax communities all over
the world are being severely damaged or destroyed by human activities. The
destruction caused by the volcanic explosion of Mount St. Helens, in the
northwestern United States, for example, pales in comparison to the destruction
caused by humans. We need to know what aspects of a community are most important
to the community’s resistance to destruction, as well as its recovery.
10. The word “pales” in the passage is closest in meaning to
○Increases proportionally
○Differs
○Loses significance
○Is common
纵深留学考试 缔造高分传奇
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Paragraph 7:Many ecologists now think that the relative long-term
stability of climax communities comes not from diversity but from the
“patchiness” of the environment, an environment that varies from place to
place supports more kinds of organisms than an environment that is uniform.
A local population that goes extinct is quickly replaced by immigrants from
an adjacent community. Even if the new population is of a different species,
it can approximately fill the niche vacated by the extinct population and keep
the food web intact.
11.Which of the sentences below best expresses the essential
information in the highlighted sentence in the passage? Incurred choices change
the meaning in important ways or leave out essential information.
○Ecologists now think that the stability of an environment is a result
of diversity rather than patchiness.
○Patchy environments that vary from place to place do not often have
high species diversity.
○Uniform environments cannot be climax communities because they do
not support as many types of organisms as patchy environments.
○A patchy environment is thought to increase stability because it is
able to support a wide variety of organisms.
纵深留学考试 缔造高分传奇
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12.The word “adjacent” in the passage is closest in meaning to
○Foreign
○Stable
○Fluid
○Neighboring
Paragraph 6: Ecologists are especially interested to know what factors
contribute to the resilience of communities because climax communities all over
the world are being severely damaged or destroyed by human activities. The
destruction caused by the volcanic explosion of Mount St. Helens, in the
northwestern United States, for example, pales in comparison to the destruction
caused by humans. We need to know what aspects of a community are most important
to the community’s resistance to destruction, as well as its recovery.
13.Look at the four squares [ ] that indicate where the following
sentence could be added to the passage.
In fact, damage to the environment by humans is often much more severe
than damage by natural events and processes.
Where would the sentence best fit? Click on a square to add the sentence
to the passage.
纵深留学考试 缔造高分传奇
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14.Directions: An introductory sentence for a brief summary of the
passage is provided below. Complete the summary by selecting the THREE answer
choices that express the most important ideas in the passage. Some sentences
do not belong in the summary because they express ideas that are not presented
in the passage or are minor ideas in the passage. This question is worth 2
points.
The process of succession and the stability of a climax community can
change over time.
Answer choices
○The changes that occur in an ecosystem from the pioneer to the climax
community can be seen in one human generation.
○A high degree of species diversity does not always result in a stable
ecosystem.
○The level of resilience in a plant community contributes to its
long-term stability.
○Ecologists agree that climax communities are the most stable types
of ecosystems.
○Disagreements over the meaning of the term “stability” make it
difficult to identify the most stable ecosystems.
○The resilience of climax communities makes them resistant to
纵深留学考试 缔造高分传奇
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destruction caused by humans.
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