[求助]周四考集中看GWD阅读分类有一篇怀疑答案错，急啊

就酱紫吧

今天看GWD阅读分类，GWD1-10觉得答案有问题，但是浏览了下似乎曾经有人讨论过，但是最终我下到的答案是那个我认为错的，所以请大家帮忙看一下，如果知道以前的讨论贴帮忙给个链接，或者帮忙给个确定的答案或理由，不尽感谢。

GWD-1-Q9 to GWD-1-Q12:

      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 effect 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.

      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. 

      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 to suspect that the effect

would be qualitatively different

than what was seen in the

aftermath 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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GWD-1-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

             

1. pristine streams that are near polluted streams become polluted themselves

2. the particular adaptations of a polluted stream’s salmon population can be preserved without dilution

3. the number of salmon in pristine habitats decreases relative to the number in polluted streams

4. an environmentally degraded stream could be recolonized by new salmon populations should the stream recover

5. the extinction of the salmon populations that spawn in polluted streams is accelerated

最新下的答案是D，没有显示有争议，我的答案是B，

理由如下：

1、题目要inferred，说明文章中没有直接说，要从文中信息推导。答案解释说D选项是文中原句：a mechanism by which a location can be repopulated should the fish there disappear.的改写（因为标注说repopulated=recolonized; disappear=recover），我不知道这两个等价对不对，但是如果是文中原句改写就肯定不是inference题的答案了瓦。

2、og说inference一般考这几种：通过两个事物的比较推出这个表较的base什么；文中说了，推出a的反面；文中说了一种effect，推导出这种effect的cause。虽然og这里是在举例，但这几种确实在inference里很常见，我认为这题的考点可以看成是已知了a，要推出a的反面。文中原话是这么说的：Low levels of straying are crucial, since the process provides a source of novel genes and a mechanism
    by which a location can be repopulated should the fish there disappear. Yet high rates of straying can be problematic because misdirected fish may interbreed with the existing stock to such a degree that any local adaptations that are present become diluted.

这里Low levels of straying和high rates of straying是对应着说的（相同颜色表示对应处），那么知道的是high rates of straying会使原来的适应性减弱，根据其反面，那个mechanism不就是能使particular adaptations be preserved without dilution么？B里的那个polluted 要是一眼看过去理解为被污染的那么B肯定就是错的了，但我认为这里指的是基因被污染的即杂交了，不是纯种了。我猜想作者觉得salmon杂交了就不好了，纯种的才好（作者的tone看最后一段的gene flaw一句），所以用了polluted这个贬义词。而且这题的focus不是污染，是disturbance，所以偶认为B对噢。

[此贴子已经被作者于2007-1-29 19:41:27编辑过]