GWD 29-9，请教

ershao

Q9:

Manatees, aquatic mammals inhabiting Florida’s rivers and coastal waters, swim close to the surface and are frequently killed in collisions with boats.  To address the problem, boat traffic in manatee-populated waters is being required to maintain very low speeds.  Unfortunately, manatees are unable to hear low-pitched sounds and a boat’s sound lowers in pitch as the boat slows.  Therefore, this approach may in fact make things worse rather than better.

Which of the following, if true, casts most doubt on the conclusion?

The areas where boats would have to maintain low speeds were decided partly on the basis of manatee-population estimates and partly from numbers of reported collisions between manatees and boats.

Because the water hyacinth that manatees feed on grows best in water that is nearly still, water hyacinth beds can be disturbed or damaged by fast-moving boat traffic.

Over the last several decades, boat traffic in Florida’s coastal waters has been increasing almost continuously and now represents the greatest threat to the endangered manatee population.

The sound of a boat engine generally travels much further under water than it does through the air.

When experimenters exposed manatees to the recorded sounds of boats moving at various speeds, the creatures were unable to discern the sounds over normal background noise.

答案给E

我认为B更好，降低船速可提高hyacinth的存活, 从而有利于manatee的存活. 因此降低船速还是有用的........

NN帮忙看看,谢谢！！！！

colleen

E is right. According to E, manatees were unable to discern the sound over normal backgroud noise. It implies manatees are able to discern the sound above the normal background noise. So if the boat speeds fast, the boat sound higher in pitch, then manatees can hear it.

五大老

我也选的B，不太明白E的意思，能不能用中文解释一下E

shanexin

以下是引用colleen在2005-12-26 13:09:00的发言：
E is right. According to E, manatees were unable to discern the sound over normal backgroud noise. It implies manatees are able to discern the sound above the normal background noise. So if the boat speeds fast, the boat sound higher in pitch, then manatees can hear it.

I don't think so. That manatees were unable to discern the sound over nomral background noise doesn't mean manatee are able to discern the sound above the normal background noise, which is false dilemma, black or white fallacy. In addition, the premise of the recognization of the sound is provided in the context.

josephhan001

选项E：Manatees不能在正常噪音背景的情况下区分不同速度的船只的声音。

证明题目中前提和结论无关，直接削弱结论。

选项B出现了题目里没有出现的因素the water hyacinth , 虽然也有削弱结论的作用，但是属于间接削弱结论。

因此要选直接削弱结论的E。

rosierosie

还是不明白!

原文说的是让船放慢速度以保护M,但是因为M听不到放慢速度的船的更低音调的声音，所以计划会使情况变坏而不使变好。

那跟E中的 various speeds有什么关系？而且这里的background sound又使指的什么那?

shzzhengfan

原文的结论是：这个方法会使情况变得更糟。削弱：没有使情况变得更糟。

原文的推理是：船速降低后，音调变小，所以动物听不见了（船快的时候能听见），所以更容易撞船了，因此情况变更糟了。

E说，船在各个速度下，这动物其实根本分不出船的声音和其他声音（可以理解为这动物就是聋的），所以船快船慢，这动物被船撞得几率是一样的，因此就不能说这个计划使情况变糟了。

不知说清楚没？

titatita

还是不太明白e为什么对

仍然支持b

[此贴子已经被作者于2006-6-9 11:16:26编辑过]

wycg

以下是引用titatita在2006-6-9 11:15:00的发言：

还是不太明白e为什么对

仍然支持b

7楼和5楼的战友说的是对的.B虽然有道理,可是它和文章说的推理无关.关于E,同意7楼的解释.

titatita

我明白了

如果没有e,b就是最好的答案.他因削弱

题目问措施使局面变得比以前更糟,只要选一个不会变的更糟的情况就行.

e说在背景噪音下,m什么声音都分辨不出.也就是说措施前,措施后没有任何变化.直接说措施不可行.直接针对原文前提,结论及推理过程.

b没有针对措施本身的问题.而说m的食物在新措施下更好.但仍然缺乏其他assumption.如果原来食物不够,现在够了,说明局面不会变得遭,但如果原来食物就过剩,现在更过剩,对m的生存不会产生任何影响.所以b不能选.