PrepTest 102

Incorrect. The conclusion is specifically about G webs that do reflect UV light, so the existence of other webs that don't is out of scope. If this discussed whether the insects were attracted to the non-reflective webs, then it might be correct.

Incorrect. The purpose of the webs is out of scope of the argument—the argument is about insect attraction to the webs, not why the webs are spun.

Incorrect. First, this answer is about other types of spiders, not the ones from the stimulus. Second, there's no indication as to whether insects are attracted to these webs—either in their entirety, or just the portions that reflect UV light.

Incorrect. This answer establishes that insects picked the G web over another web when they both reflected UV light. This suggests it's something else about the G web that attracts insects, weakening the argument.

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Insects are attracted to UV light. Insects are attracted to G spiderwebs. G spiderwebs reflect UV light.
Conclusion - Insects are attracted to G webs because of the UV light.

Answer Anticipation:
Strengthen questions have one flaw more frequently than any others—Correlation/Causation flaws. Somewhere around 50% of questions of this type have this type of flaw.

Here, the conclusion is absolutely causal—the insects are attracted to these spiderwebs "because of" the UV light they reflect. This is based on insects being attracted to UV light, and insects being attracted to the G webs, which give off UV light.

However, it's possible that there's something else that attracts the insects to these webs, and the UV light is just a coincidence. Since the argument jumps from a correlation to causation, we can strengthen it using a set list of potential answers:
(1) Eliminate an alternative cause (e.g., there's a smell the webs have that attract insects)
(2) More examples of cause/effect going together
(3) A control group - an example of no cause/no effect

Answer Explanation:
This answer strengthens the argument by combining the second and third methods. The experiment created a situation where the only difference between two G webs was whether there was UV light being reflected, and the insects went to the web with UV light. That suggests that, all else being equal, it's the UV light attracting insects, not something else (where the insects would have been split between the webs), thus strengthening the causal conclusion.

Key Takeaway:
In a Strengthen question, always be on the lookout for a Correlation/Causation flaw, as it's the most common flaw in the question type. When it's present, there's a set of likely answer choices you can look for, making your job a lot easier.