IMO - A

The answer needs to weaken Scott's claim that the warbler has been declining because the spruce budworm has been dropping. We can either find something that attacks this specific hypothesis or we can find an alternative explanation.

A does this. A says that another species of bird that does not rely on budworms is also dependent on the coffee plantation. This species of bird is declining as well. This gives us an alternative explanation.

B is irrelevant as it only tells us why the budworm population has dropped

C is irrelevant as it only tells us the timeframe for the budworm population drop

D is interesting. It offers an alternative to what the Tennessee warblers have been doing. But Scott's claim is that the population is dropping because the budworm is dropping. We can not infer from this answer that the population is dropping at all. We only know that they have begun to go somewhere else. This doesn't necessarily refute Scott's claim.

IMO: A
choice A and D are tempting.. I eliminated choice D bcuz the main focus of choice D is Tennessee warbler while the focus of Scott's reasoning is on Budworms ==> choice A makes more sense.. that is, choice A states that other songbirds population that do not hunt budworms is also declining besides their appearance also depends on coffee plantation trees

I had to respond to this one. CR reasoning and songbirds two of my favorite subjects.

Okay, so we are trying to weaken Scott's hypothesis. Notice that each of the two speakers is offering a cause for the observed effect. They are not debating the effect - declining Tennessee Warbler numbers. Rather they are debating the cause of this effect.

Scott's potential cause is the lower numbers of "spruce budworm." There are three ways to weaken this cause. You can show an alternate cause. This is the most common way to weaken a cause explanation. (In fact, that is how Scott is trying to weaken Kate's suggested cause.) The other ways are to show that the cause exists without the effect and to show the effect happening without the cause.

The correct answer choice - A - shows the effect without Scott's cause (but with Kate's cause). The Baltimore Oriole is also declining (so the effect is there) but the Oriole does not eat the spruce budworm. So this weakens Scott's conclusion. At the same time it strengthens Kate's conclusion because the Oriole does rely on the coffee plantations.

Choice D does not show that the changes in the coffee plantations are causing a decline. Sure the warblers are migrating to other places, but that might occur without a decline in population. The same way that people might stop going to a particular restaurant. It could be that those patrons just quit eating but it could be that they are going to other restaurants.

Look for cause and effect reasoning and those three ways to weaken...

Good Question ..