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## In a polluted area around the Great Lakes

BTGmoderatorDC Moderator
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#### In a polluted area around the Great Lakes

Mon Nov 27, 2017 3:23 am
In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

What is wrong with Options C and D?

OA D

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DavidG@VeritasPrep Legendary Member
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Fri Dec 01, 2017 7:12 am
lheiannie07 wrote:
In a polluted area around the Great Lakes, scientists studying bird populations have observed a drop in the number of both herring gulls and terns. Both bird species prey on the same type of fish, whose numbers are also being negatively affected by pollution. However, the tern population has seen a much sharper decrease than the herring gull population. Scientists have concluded that the herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

Which of the following, if true, would provide the best piece of evidence in support of the researchers' conclusion?

A) A survey shows that bird populations in areas around the Great Lakes have shown similar decreases.
B)A related study finds that fish populations in the Great Lakes are affected as much by other predators as by pollution.
C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.
D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.
E)Analysis of water in the area where the birds nest reveals that toxin levels are actually slightly below fish tolerance levels.

What is wrong with Options C and D?

OA D
The scientists' conclusion: The herring gulls have a higher survival rate because they've found alternative food sources.
The premise: The fish that gulls and terns feed on has been adversely impacted by pollution. The tern population has decreased by more than the gull population

So we want an answer choice that substantiates the claim that gulls have found an alternative food source. This is exactly what D gives us..Even though the fish they usually feed on are dying, we know they're eating human food. (Of course, this is a little weird, as humans eat fish, but the implication is clear - there's some kind of food that heretofore, only humans ate, and now gulls appear to eating this food too.)

C is irrelevant. Why would it matter how far the largest garbage dump is from the lake? Is 3 miles far for birds? Close? Would it be different if it were 5 miles away or 1 mile away? What about the second largest dump? The distance here doesn't tell us if the gulls are finding an alternative source from the garbage dump, and this is what concerns us.

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VJesus12 Master | Next Rank: 500 Posts
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Thu Nov 30, 2017 10:22 am
I also would like to know what is wrong with option C. Experts, may you give us some help. Thanks.

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