请教 GWD29-9 没有以前的贴

glitters

                       GWD29-9                                                                
                                                          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?

A.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.
B.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.
C.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.

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

E.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.

不太明白为什么E对，另外为什么B不对呢？谢谢！

chenzhen1858

谢谢这样削弱了啊！！！

rongyang114

so long

双鱼游

在一个网站找到的解释，非常好

Explanation:

The most important thing is to separate the premiseand the conclusion and focus on them only. Youcan then easily answer the question. You willgrasp it as you practise and practise.

Premise: Lowering the speed of the boats causelowering of the pitch of the sound

This can be stated as, Speed lowers=>itch lowers - (1)

Conclusion: Detection of boats decreases as thepitch of the sound is lowered implying collisionincreases which can be written as

Pitch lowers=>Detection more difficult - (2)

From (1) & (2) we have,

Speed decreases => Detection more difficult -(3)

We also have,

Detection more difficult=> Collision increases -(4)                                            

(Why (4) is not the main conclusion?We will talk about that later.)

The best answer is that which falsifies one of thefirst three relations.

Only E does that by falsifying (3). Iteffectively says that the detection of the boat

(i.e., discernment of the sound) by the manatees doesnot decrease with the decreasing speed butis actually indifferent to various speeds.

It is not D because the distinction between thedistance travelled by sound in air or watercannot falsify any of the three relationsbecause that issue is not at all addressed

there. Similarly other choices can be ruled outRemember to focus only on the premise and the conclusion.Anything is relevant only if it affects thepremise or the conclusion.



Tip: How would you separate premise from conclusion?

We explain one useful way of doing it.In other questions we talk about other ways.

Conclusion is something which does not logicallyfollow from the premise. It needs  assumptionsIn the above question, (4) is not considered asthe main conclusion because it logically followsfrom the argument. That is, it need not bebe explicitly stated. Detection decreseslogically implies collision increases.Even if the author doesn't state it, it isunderstood. So, instead of (4), we have (2) as theconclusion and is not part of the premise.Also consider, the example

Fact:He passed the exam.

Now the sentence: "He is intelligent" may be considereda conclusion because it is not implied from the Fact.It needs the assumption:"Those who pass theexam are intelligent". However the sentence:"He appearedfor the exam" is not a conclusion as itcan be deduced without any assumption. It iscalled an inference and is part of the Factin this exampleThere are other ways in which we can identify the premise and the conclusion whichwe discuss in the course material.

wwhappy

如果是B的话，还要加上 water hyacinth对manatees的影响的描述才行啊，这里楼主已经自行添加了假设，water hyacinth会使得manatees增加，所以还是E好

gracezz

顶一下，和LZ一样的思路选了B。。。。

glitters

同意你说的D。可我怎么觉得B是从另一方面提出了减速的一个好处呢，因为能让海牛更好的FEED，我觉得有好多这种思路的题。
我那天犯晕了，那逻辑贴到这了，不好意思。。。

BLinging

这是个逻辑题哈，你贴错了，贴到语法专区了。

这个就是说：海牛总是死于船只相撞。为了减少这个问题，就让船慢慢开。但是船慢了声音会比较低，所以海牛听不到比较低的声音，所以造成的后果更糟。
E weaken的是说，船无论快慢，海牛都听不到，所以造成的结果不会更糟（虽然也不会更好）。
B是一个无关选项。