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CR weaken - baja turtles

Expert replies
by vishalwin » Fri Dec 04, 2015 11:34 pm
Loggerhead turtles live and breed in distinct groups, of which some are in the Pacific Ocean and some are in the Atlantic. New evidence suggests that juvenile Pacific loggerheads that feed near the Baja peninsula hatch in Japanese waters 10,000 kilometers away. Ninety-five percent of the DNA samples taken from the Baja turtles match those taken from turtles at the Japanese nesting sites.

Which one of the following, if true, most seriously
weakens the reasoning above?

(A) Nesting sites of loggerhead turtles have been
found off the Pacific coast of North America
several thousand kilometers north of the Baja
peninsula.

(B) The distance between nesting sites and feeding
sites of Atlantic loggerhead turtles is less
than 5,000 kilometers.

(C) Loggerhead hatchlings in Japanese waters have
been declining in number for the last decade
while the number of nesting sites near the
Baja peninsula has remained constant.

(D) Ninety-five percent of the DNA samples taken
from the Baja turtles match those taken from
Atlantic loggerhead turtles.

(E) Commercial aquariums have been successfully
breeding Atlantic loggerheads with Pacific
loggerheads for the last five years.




Can you please explain choices C and D. I didn't get why OA is D and not C.



My reasoning:

Conclusion: " Baja turtles match those taken from turtles at the Japanese nesting sites."

My aim in this question is to weaken the conclusion and "I should see an answer that says BAJA turtles and JAPANESE SITE turtles are different and have DNA SIMILAR TO match those taken from Atlantic loggerhead turtles.

Then I read option C and it says hatchlings in Japanese water have been declining while that of BAJA peninsula is constant. That's why C sounds better than D.


Then, Initially I choose option D because it gives me an alternate reason that BAJA turtles and JAPANESE SITE turtles are different and BAJA turtles DNA

Source: powerscore GMAT CR book.
Thanks & Regards
vishalwin
------------------------------------
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Source: — Critical Reasoning |

by MartyMurray » Sat Dec 05, 2015 4:17 am
(A) Nesting sites of loggerhead turtles have been
found off the Pacific coast of North America
several thousand kilometers north of the Baja
peninsula.

This argument is based on DNA data that suggest that the turtles that feed near the Baja peninsula come from Japanese waters. The fact that there is another nesting site closer to the Baja peninsula does not really weaken this DNA data based argument.

(B) The distance between nesting sites and feeding
sites of Atlantic loggerhead turtles is less
than 5,000 kilometers.

This is interesting, and may suggest that the conclusion is incorrect, but it does not attack DNA based path to the conclusion.

(C) Loggerhead hatchlings in Japanese waters have
been declining in number for the last decade
while the number of nesting sites near the
Baja peninsula has remained constant.

This is a trick answer. The prompt is about the DNA of juveniles feeding off the Baja peninsula. This answer choice discusses nesting sites near the Baja peninsula. Either the DNA data connects the juveniles to the hatching sites near Japan or it does not, and the fact that the number of nesting sites off the Baja peninsula is constant does not tell us whether this connection is sound.

Another way to look at this is that there could be two nesting sites off the Baja peninsula and 1000 near Japan. So the fact that there are nesting sites off the peninsula may be insignificant.

Further, hatchlings from the Baja peninsula nesting sites could go elsewhere to feed as juveniles.

(D) Ninety-five percent of the DNA samples taken
from the Baja turtles match those taken from
Atlantic loggerhead turtles.

This directly attacks the argument. The Atlantic loggerheads, which clearly do not come from waters near Japan, have DNA that matches that of the hatchlings from waters near Japan as much as the DNA from the juveniles feeding off the peninsula does. This seems to totally destroy the argument that matching DNA can be used to determine origin.

(E) Commercial aquariums have been successfully
breeding Atlantic loggerheads with Pacific
loggerheads for the last five years.

This tells us nothing that undermines the conclusion that the turtles feeding off the Baja peninsula come from waters near Japan.

So the best answer is D.
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