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虽然我做错了,但是经过好长时间的分析,还是支持选C, 分析如下: 第一段文章先说人类活动对于salmon的生存环境有影响,后来写 Indeed, most analysts believe that some kind of environmental degradation underlies the demise of many extinct salmon populations。这就说明自然环境对马哈鱼的灭绝也有影响。 第二段开始说火山爆发的影响 Straying rates remain relatively low when environmental conditions are stable, but can increase dramatically when streams suffer severe disturbance. The 1980 volcanic eruption of Mount Saint Helens, for example 这就说明了这种环境的影响 第三段开始说Although no one has quantified 定量化的changes in the rate of straying as a result of the disturbances caused by humans, there is no reason to suspect that the effect would be qualitatively 性质上的different than what was seen in the aftermath of the Mount Saint Helens eruption. 就是说人类的影响与环境的影响没有明确的质量上的对比,但是性质上是不同的,那么两者谁严重呢?
看看文章中的第一段,人类的影响是there are fewer salmon in degraded regions than in pristine ones,但是第二段中说环境比如火山爆发的影响是 Large-scale……even if those areas have pristine habitats.就是说在 pristine 的地方都会受到影响,所以火山爆发这种大规模的环境破坏影响更大一些
因此, Mount Saint Helens eruption 的影响可以作为which 人类活动 should be measured的一个标准,也就是C所说provide a standard of comparison against which the impact of human activity on the gene flow among salmon populations should be measured 这里只是对比关系,并没有量上的等价关系。
而B 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 这里的extent就说明了等于关系,并且文章中根本就没有比较过 in one stream 的破坏而对于 elsewhere 的马哈鱼的影响,也没有说他们的基因结构产生了什么变化,连参照物都不明确就谈不上比较。可以说B根本就是无关选项
所以选择C,这是我的拙见,欢迎抛砖 |
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