patto wrote:
Last winter was mild enough to allow most bird species to forage naturally, which explains why the proportion of birds visiting feeders was much lower than usual. The mild winter also allowed many species to stay in their summer range all winter without migrating south, thereby limiting the usual attrition accompanying migration. Hence, last year’s mild winter is responsible for this year’s larger-than-usual bird population.
Which one of the following, if true, would most strengthen the reasoning in the argument?
(A) Increases in bird populations sometimes occur following unusual weather patterns.
(B) When birds do not migrate south, the mating behaviors they exhibit differ from those they exhibit when they do migrate.
(C) Birds eating at feeders are more vulnerable to predators than are birds foraging naturally.
(D) Birds that remain in their summer range all winter often exhaust that range’s food supply before spring.
(E) Birds sometimes visit feeders even when they are able to find sufficient food for survival by foraging naturally.
Premises:
Last year's mild winter led to more natural foraging and less feeder visiting.
Last year's mild winter also led to no migration and hence limited the accompanying reduction in numbers.
Conclusion: Last year’s mild winter is responsible for this year’s larger-than-usual bird population
We need to strengthen that mild winter is the reason behind larger than usual bird population right now.
(A) Increases in bird populations sometimes occur following unusual weather patterns.
We need to strengthen that mild winter led to increase in bird population. We don't know what unusual weather pattern is being talked about here. Also, we are given that SOMETIMES unusual weather pattern leads to increase. Is it one of those times, we don't know.
(B) When birds do not migrate south, the mating behaviors they exhibit differ from those they exhibit when they do migrate.
We don't know how the mating behaviour differs. Do they multiply faster or slower? - Does not tell us.
(C) Birds eating at feeders are more vulnerable to predators than are birds foraging naturally.
This tells us that birds foraging naturally are less likely to be killed by predators. We know that mild winters led to more natural foraging and less feeding at feeders. So this helps strengthen that mild winters led to a higher bird population this time.
(D) Birds that remain in their summer range all winter often exhaust that range’s food supply before spring.
Irrelevant. What will happen in spring is not our concern.
(E) Birds sometimes visit feeders even when they are able to find sufficient food for survival by foraging naturally.
Doesn't help strengthen our conclusion. Even if some birds visited feeders, the number was less than before and that the argument tells us. It doesn't help connect mild winter with increase in bird population.
Answer (C)
At best, option C strengthen the "Conclusion". But it doesn't seem to strengthen the "Reasoning" the question is asking for. The reasoning is that because of limitation in migration the population increased, and the option C doesn't reinforce this argument, but put forwards another reasoning for the outcome.