Critical reasoning is not my specialty, but let me give this a try.


"Crows, herring gulls, and sparrows all live on the island of Firsten."
There are three types of birds to consider: crows, gulls, and sparrows.

"Crows feed on sparrow eggs and therefore pose a threat to the sparrow population."
Crows are a threat to the whole sparrow population. This sounds serious.

"Although gulls are not nearly as good at finding sparrow nests as crows are, sparrows typically also lose some eggs to gull predation."
Although gulls are not a threat, they still eat sparrow eggs.

"Nevertheless, sparrows that nest near gull nests tend to lose fewer eggs to predators than sparrows nesting far away from gull nests, since____"
So why are they building their nest closer to the gulls who eat their eggs?!?

In terms of danger to the population of sparrows: crows > gulls. Gulls eat sparrow eggs but since they have a hard time finding the nests, they don't eat as many eggs and aren't that much of a danger (threat) to the sparrow population. To finish the sentence, we need to find a reason why building nests near gulls allows them lose fewer eggs.


Which of the following most logically completes the argument?
A. the presence of gulls frightens away Crows
The crows are a threat to the sparrows, while the gulls sometimes eat their eggs. If the gulls scare away the threat (the crows), then fewer eggs would be lost because only the gulls who have trouble finding sparrow nests are able to prey on them.

B. crows pose no threat to adult sparrows
This doesn't matter. Crows are eating the eggs, not the sparrows.

C. gulls find sparrow nests by watching female sparrows enter the nest
It says gulls have a difficult time finding the sparrow nests. If the nests were closer to the gulls and it was easier to find the nests, then living near the gulls would make the sparrows a threat. In the passage, it implies that they are not a threat

D. there are far more crows on Firsten than there are sparrows
This is out of scope and has no relation to why sparrows would lose less eggs nesting near gulls than otherwise.

E. sparrows on Firsten typically hide their nests very carefully
Trap answer. This would explain why it's ok for sparrows to build nests near gulls, but it doesn't address this issue of why they lose less eggs when they do. Unlike the gulls, the crows have no problem finding the sparrow nests.