Fire ants from Brazil now infest the southern United States. Unlike queen fire ants in Brazil, two queens in the Unit...

shunhe on August 11, 2020

Hi @Harper,

Thanks for the question! So let’s go over the stimulus real quick. We’re told about fire ants in the southern US that are basically bad. In Brazil, there are predator insects that feed on them and limit the population, so the argument concludes that bringing these into the US would overall benefit the environment by stopping the increase of the fire ant population in the US.

Now we’re asked for something that’s NOT an assumption made in the argument. So the correct answer choice should be something that’s not necessary for the argument to assume. Take a look at (D), which tells us that the predator insects would stop the increase of the ant population before the ants spread to states that are further north. Was anything ever said or assumed about the timescale, that this happens before or after the ants go farther north? No, not at all. And we can use the negation test to confirm that this isn’t a necessary assumption. Let’s say it’s not true that the predator insects would stop the increase of the ant population before the ants spread farther north; in other words, they didn’t stop them until after they spread farther north. Does that hurt the conclusion, that bringing in these predators would overall benefit the environment by stopping the increase of the fire-ant population? No, not at all, and so we know this isn’t a necessary assumption and thus the correct answer.

(C), on the other hand, is an assumption the argument makes, that the especially aggressive fire ants from the two-queen nests wouldn’t be able to destroy the Brazilian predator insects. Let’s try the negation test to see if this is a necessary assumption; does it weaken the argument if the fire ants can destroy the Brazilian predator insects? Yes, it does, because then it’s probably not true that the predator insects would be able to stop the increase of the fire-ant population in the US. So since negating (C) damages the argument, it’s a necessary assumption, and the wrong answer for this “except” question.

Hope this helps! Feel free to ask any other questions that you might have.