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Every fall Croton's jays migrate south. The jays always join [#permalink]
17 Feb 2009, 00:36
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Every fall Croton's jays migrate south. The jays always join flocks of migrating crookbeaks with which they share the summer and winter territories. If a jay becomes separated from the crookbeaks it is accompanying, it wanders until it comes across another flock of crookbeaks. Clearly, therefore, Croton's jays lack the navigational ability to find their way south on their own.
Which of the following, if true, most strengthens the argument above? A - Croton's jays lay their eggs in the nest of crookbeaks, which breed upon completing their southern migration. B - The three species of most closely related to crookbeaks do not migrate at all. C - In the spring, Croton's jays migrate north in the company of Tattersall warblers. D - Species other than Croton's jays occasionally accompany flocks of migrating crookbeaks. E - In the spring, crookbeaks migrate north before Croton's jays do.
I narrowed it down to C and D, and picked C based on the assumption that the jays always need someone to migrate with, hence,
Conclusion: The jays can't navigate south on their own. Evidence: Share migration with crookbeaks, if jay is lost :: jay finds crookbeaks Assumption: The jays always migrate with birds of a differing species.
Not sure if this is entirely the correct reasoning...guess I would've been a little lucky.
The premise they want us to strengthen is that these C Jay birds lack the ability to find their way on their own. C is the only one that strengthes this premise.
C says (C) In the spring, Croton’s jays migrate north in the company of Tattersall warblers.
If these birds also migrate following another type of bird this supports the premise that they cannot find the way on their own.
The reason it is not A is because -
A says Croton’s jays lay their eggs in the nest of crookbeaks, which breed upon completing their southern migration. Well, this provides a different reason as to why they would follow the crookbreaks. They might be following them because they are waiting for their young to be born, not because they lack the navigational ability to find their way south on their own.
The reason it is not B is because - B says B) The three species of most closely related to crookbeaks do not migrate at all
This is irelevant and has nothing to do with the argument.
The reason it is not D is because -
D says, (D) Species other than Croton’s jays occasionally accompany flocks of migrating crookbeaks.
This statement does not strengthen the premise that Croton Jays' can't follow directions. It actually weaknes that premise because it shows that other birds also follow these birds, so it is not a specific condition for the the C Jays.
E is not the answer, because it is not relevant to the question
Well, think of this: if CJ do not follow CB when migrating north and follow another species instead, how would CJ find CB to share the north habitation areal with? Thus, C weakens the statement. The right answer is D: it emphasizes the leadership of CB among the migrating species.