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.

I marked the OA by PoE, but I was not much clear on the argument. Can someone explain on the argument and answer choice?
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D

IMO B.
water hyacinth beds can be disturbed or damaged by fast-moving boat
traffic. when Boats maintain low speeds, it cant worsen things.

OA?

E...if they cannot distinguish different boat sounds, there won't be much difference (the situation will maybe improve), and the conclusion is weakened...

E IMO We are supposed to logically negate the argument. E does that by making the stituation from worse ------ > Same .

QA plz ?
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Finally KISSedGMAT 700 times 450 to 700 An exprience

What is a shell game? How is it affecting the argument?


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E

OA is E. Good catch by krypt.
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E.
Seemed easy to me.

because boats drive fast they kill manatee.
Why? there are two reasons: either manatees are sluggish or deaf.
conclusion: author says that deafness kills M. we must introduce evidence that would make author to reconsider his her conclusion by saying "ohh... I am stupid I did not account for this"

E says that M can't discern sounds, so they die not due to deafness, but becuase they are sluggish.
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i also thought B
but E it shud be
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