PrepTest 111

Incorrect. The stimulus notes that not all insect species are bad—some are pests, but others eat pests. As such, harming a greater number of species isn't necessarily a benefit of chemical insecticides over B.t., and thus this doesn't weaken the argument.

Incorrect. First, there's no indication that chemical insecticides are effective against all insects. Second, there's no indication that there aren't strains of B.t. that can control all insects, thus making it a viable option. Third, there's no indication that a single strain of B.t. isn't effective against the vast majority of insects, only failing to control a few very rare ones. Fourth, this answer is about insects, whereas the goal is to control pests—it's possible that B.t. isn't effective against all insects, but it is against all pests. There are many reasons to eliminate this answer!

Incorrect. The goal of these insecticides are to harm insect pests, so failing to control weeds doesn't address their goal. Additionally, there's no indication that chemical pesticides harm weeds, so this answer wouldn't provide a reason to believe that the B.t. isn't as good as the chemicals.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Weaken

Stimulus Summary:
B.t. is better than chemical pesticides because:
(1) It's specific to insect pests, not harming the insects that prey on them
(2) It doesn't hurt mammals/birds
So using B.t. is preferable to using chemical pesticides

Answer Anticipation:
This argument is all about the comparison between B.t. and chemical pesticides. It lists some reasons that the former is preferable to the latter before reaching that conclusion.

Whenever an argument compares two things, check to see if it's a "fair" comparison—does the author list the pros and cons of both sides, and then establish a principle that tells us which of the pros/cons is the one that should determine the superior option? Here, the author doesn't—there's no exploration of the pros of the chemical pesticides, nor is there a principle stating that any of the individual pros of B.t. is determinative.

It'd be hard to weaken this argument with a principle since we are only provided with benefits of B.t., so any principle wouldn't really make that option seem worse. As such, it's likely that the correct answer will weaken the conclusion here by providing a relative benefit of chemical pesticides over B.t.

Answer Explanation:
This answer provides a relative disadvantage of B.t. over chemical pesticides, thus weakening the conclusion that the former is preferable to the latter.

Key Takeaway:
When an argument compares two things and determines that one is "better", it needs to establish a principle by which that determination can be made, and then compare the two over the metric in the principle. When this happens in a Weaken question, the correct answer generally brings up a relative downside of the "better" option over the "worse" one.

Incorrect. This answer might provide a reason to focus on birds and rodents separately, but it doesn't provide a reason to go with B.t. or chemical pesticides over the other to control the insect pests that are damaging crops.