The conclusion of the study cited in the stimulus is "that there is a definite relationship between climate and the population size of finch species that thrive at various times." How do we know this? We are given information about what occurs during droughts and what occurs during rainy years.
This is a Strengthen with Necessary Premise question so we are looking for the answer choice that not only strengthens the argument, but that also is necessary to the argument.
Let's take a look at answer choice (B), which states "a lengthy period of rainy weather results in fewer large, hard seeds being produced." This clearly strengthens the argument by showing that the primary food supply for large finch species during droughts is not available in rainy years. Now let's negate (B) to make sure that is it also necessary to the argument.
The negation of (B) would be, "a lengthy period of rainy weather does not result in fewer large, hard seeds being produced." Notice that this would destroy the argument's conclusion because the difference in survival rates of small and large finches could not be described by the climatic variations because the large, hard seeds that large finches eat during droughts are still available during lengthy periods of rainy weather.
Hope this helps! Please let us know if you have any other questions.
rolltribeSeptember 1, 2015
Why can't E be correct?
NazSeptember 3, 2015
The issue with (E) is that it does not strengthen. We know nothing about the characteristics of the small seeds. It is possible that they have softer skin, which the small finches can easily crack open even with their small beaks.
So, whether or not the small seeds have to be cracked open in order to be digested does nothing to our argument because we do not know anything about these small seeds. It's very possible that small finches have no issue at all cracking open the small seeds.
Hope that helps! Please let us know if you have any other questions.
alymathieuNovember 22, 2018
Why wouldn't d be correct
RaviDecember 21, 2018
@alymathieu,
D is not a premise that must be assumed in order to justify the conclusion. D would provide support for the overall accuracy of the data in the study, but it doesn't do anything to help us fill the argument's hole regarding why the larger finches don't do as well in moist seasons. If they could do well in droughts with the big seeds, why can't they do well in moist seasons?
Answer B picks up on this, and as Mehran points out above, if we negate answer B, the argument falls apart.
Hope this helps. Let us know if you have any other questions!
grimadeauMay 18, 2020
Why can't it be answer choice c?
TreJuly 9, 2021
While answer choice (B) seems like it would strengthen, it doesn't seem as if it would be necessary that there were fewer of the large, hard seeds "produced." It seems that it could be the case that there are NOT fewer of them produced, just that maybe members of the large finch species are not able to access them as well as they did in drought conditions. Hypothetically, maybe the plants that produce these seeds grow in areas that the finches cannot reach in rainy years but can in drought conditions. Regardless, I do see how this would be preferable to the other choices available. But am I off on how I interpreted what was necessary for the conclusion here?
