2017-08-12 440阅读
以下将为正在备战GMAT考试的同学们整理一些经典的GMAT阅读试题,并分多个合集推出,希望能够为正在备考GMAT考试的考生提供或多或少的帮助。
Over the last 150 years, large
stretches of salmon habitat have
been eliminated by human activity:
Line mining, livestock grazing, timber
(5) harvesting, and agriculture as well
as recreational and urban devel-
opment. The numerical fect is
obvious: there are fewer salmon
in degraded regions than in pris-
(10) tine ones; however, habitat loss
also has the potential to reduce
genetic diversity. This is most
evident in cases where it results
in the extinction of entire salmon
(15)populations. Indeed, most
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. 提出现象:数量减少,基因多样性下降,因为环境问题
Large-scale disturbances in
(25)one locale also have the potential
to alter the genetic structure of
populations in neighboring areas,
even if those areas have pristine
habitats. Why? Although the
(30)homing instinct of salmon to their
natal stream is strong, a fraction
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 high rates
of straying can be problematic
because misdirected fish may
interbreed with the existing stock
(45)to such a degree that any local
adaptations that are present
become diluted. Straying
rates remain relatively low when
environmental conditions are
(50)stable, but can increase dramati-
cally when streams suffer severe
disturbance. The 1980 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
straying, initially 16 percent,
rose to more than 40 percent
(65)overall.另外后果及原因:干扰同样导致基因结构变化,因为洄游路线频率上升
Although no one has quantified
changes in the rate of straying
as a result of the disturbances
caused by humans, there is no
(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.最终结果:后代适应性变差
结论解释
逻辑简图:
1P:samlon habitat eliminated by… fect obvious: fewer; however, reduce genetic diversity
2P: also alter genetic structure. Low crucial; yet high, problematic.
3P: although, no reason to suspect…. Increase result in, in turn lower the …..
相关链接:
1.浅析GMAT阅读的提升技巧
2.GMAT备考经验分享:不要忽视阅读和逻辑(一)
3.GMAT阅读解题技巧:抽象词速度法
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