Q9 to Q12:
Over the last 150 years, large
stretches of salmon habitat have
been eliminated by human activity: 提出一个观点:人类行为影响三文鱼聚集地 (人为因素)
Line mining, livestock grazing, timber
(5) harvesting, and agriculture as well
as recreational and urban devel-
opment. The numerical effect is 人类行为的几种明显的作用
obvious: there are fewer salmon
in
degraded[I1] [I1] regions than in pris-
(10) tine ones; however[I2] [I2], habitat loss
also has the potential to reduce
genetic diversity. This[I3] [I3] is most
evident in cases where it results
in the extinction of entire salmon
(15) populations. Indeed[I4] [I4], most 环境对S的影响.(环境因素),下面会针对这个结论作出解释
analysts believe that some kind
of environmental degradation
underlies the demise of many
extinct salmon populations.
(20) Although some rivers have
been recolonized, the unique
genes of the original populations
have been lost.
Large-scale disturbances in
(25) one locale also
have the potential[I5] [I5]
to alter the genetic structure of
populations in neighboring areas,
even if those areas have pristine
habitats. Why?[Y6] [Y6]
Although the
(30) homing instinct [I7] [I7]of salmon to their
natal stream is strong, a fraction 一地环境改变对另一地的物种影响(环境因素)
of the fish returning from the sea
(rarely more than 15 percent)
stray and spawn in nearby
(35)
streams. Low levels of straying
are crucial, since the process
provides a source of novel
genes and a mechanism
by which a location can be
(40) repopulated should the fish
there disappear. Yet[Y8] [Y8]
high rates
of straying can be problematic
because misdirected fish may
interbreed
[I9] [I9]with the existing stock
(45) to such a degree that any local
adaptations that are present
become diluted[I10] [I10]. Straying
rates remain relatively low when
environmental conditions are
(50) stable, but can increase dramati-
cally when streams suffer severe
disturbance[I11] [I11]. The 1980[I12] [I12] volcanic
eruption of Mount Saint Helens,
for example, sent mud and debris
(55) into several tributaries of the
Columbia River. For the next
couple of years, steelhead trout
(a species included among the
salmonids) returning from the
(60) sea to spawn were forced to
find alternative streams. As
a consequence, their rates of
as a consequence 提出结论了.
straying, initially 16 percent,
rose to more than 40 percent
(65) overall.
Although no one has quantified
changes in the rate of straying
as a result of the disturbances
caused by humans, there is no
(70) reason[I13] [I13] to suspect that the effect
would be qualitatively different 这里作者说,没有理由怀疑人为因素的影响在质量上和MSH eruption是不同的,
than what was seen in the
aftermath[I14] [I14] of the Mount
Saint
Helens eruption. Such a dra-
(75) matic increase in straying from
damaged areas to more pristine
streams results in substantial
gene flow, which can in turn lower
the overall fitness of subsequent
generations.
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Q9:
The primary purpose of the passage is to
- argue against a conventional explanation for the extinction of certain salmon populations and suggest an alternative
- correct a common misunderstanding about the behavior of salmon in response to environmental degradation caused by human activity
(作者也是不否认人为行为的) - compare the effects of human activity on salmon populations with the effects of natural disturbances on salmon populations
- differentiate the particular effects of various human activities on salmon habitats
(以偏盖全,只在第一段而已) - describe how environmental degradation can cause changes in salmon populations that extend beyond a numerical reduction (本文是典型的结论解释类型的文章)
(E)
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Q10:
It can be inferred from the passage that the occasional failure of some salmon to return to their natal streams in order to spawn provides a mechanism by which
- pristine streams that are near polluted streams become polluted themselves (原文没提到)
- the particular adaptations of a polluted stream’s salmon population can be preserved without dilution
- the number of salmon in pristine habitats decreases relative to the number in polluted streams
- an environmentally degraded stream could be recolonized by new salmon populations[Y15] [Y15]
should the stream recover - the extinction of the salmon populations that spawn in polluted streams is accelerated
(D)
从选项里找出: 鱼为了排卵而想回到他们本身的生存地带却失败了的原因.
定位: L35-41
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Q11:
According to the passage, human activity has had which of the following effects on salmon populations?
- An increase in the size of salmon populations in some previously polluted rivers
- A decline in the number of salmon in some rivers
- A decrease in the number straying salmon in some rivers
(环境因素) - A decrease in the gene flow between salmon populations that spawn in polluted streams and populations that spawn in pristine streams
- A decline in the vulnerability of some salmon populations to the effects of naturally occurring habitat destruction
(B)
定位: L1-7
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Q12:
The author mentions the “aftermath of the Mount Saint Helens eruption” (lines 73-74) most likely in order to
- provide an example of the process that allows the repopulation of rivers whose indigenous salmon population has become extinct
- indicate the extent to which the disturbance of salmon habitat by human activity in one stream might affect the genetic structure of salmon populations elsewhere
- provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured
(能不能被measured和文章信息无关) - show how salmons’ homing instinct can be impaired as a result of severe environmental degradation of their natal streams
- show why straying rates in salmon populations remain generally low except when spawning streams suffer severe environmental disturbance
(B)
定位: L65- 75 (这条题和下面宝儿说的答案有区别,我是倾向于选B的,因为C的be measured是无关信息我觉得)
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发表于 2007-10-2 15:18:00
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