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.

Why 'D' and Why not 'C' ?
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Thriving for CHANGE

Hi Aristocrat,

Compare the two choices which are two contenders for strengthening the conclusion

C) Maps of the area reveal that the largest garbage dump in the area is located 3 miles inland from the lake.

Map is a hard evidence that says the largest garbage dump in the area is located 3 miles inland from the lake. which indirectly refutes the premise that herring gulls have a higher survival rate because they are able to find alternative sources of food, including garbage dumps along the shoreline.

And as premise is taken by its words, we cannot the refute the same.


whereas

D) Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food.

Strengthens the arg. conlcusion that the birds are getting their food from the waste irrespective of what the source of the food is.


Pls let me know if i'm missing a pt here.

Thanks

How 'C' refutes an argument.
it may be supporting that because of close proximity of garbage dump.
birds might be feeding on them.
_________________

Thriving for CHANGE

Hi Aristocrat,

I'll focus here on the main pt of the argument.Pls let me know if i'm incorrect here.

Premise : Because they (gulls) are able to find alternative sources of food, including garbage dumps along the shoreline.

Conclusion : Scientists have concluded that the herring gulls have a higher survival rate

Assumption: Food found from alternative source/garbage dump is consumable by birds leading to higher survival rate.

Hence D strengthens the arg. saying that "Blood tests performed on the gulls reveal high levels of the types of fatty acids generally found only in human food."


As per my understanding considering the factor of location is out of scope here.

Also C says that garbage dump is 3 miles inside.

As it involves assuming that whether the distance of 3 miles is near or farther. Hence it could be refuting/strengthening the argument depending upon the assumption under consideration.

Thanks
Jatin