PrepTest 134

Incorrect. If this answer stated that they weren't exposed to heavy metals, then it might be an example of a "control" that could strengthen the argument. However, it's about heavy metal resistance, which would be a step away from the correlation that would help the argument. A correlation to a correlation is just too tenuous to affect an argument!

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
There are a lot of heavy metals in sewer sludge. Bacteria that survive there have resistance to heavy metals. They also have resistance to antibiotics. So the heavy metals make bacteria resistant to antibiotics.

Answer Anticipation:
The conclusion of this Strengthen question features causal language—"has somehow promoted"—so we should check for a correlation/causation flaw. Why does the Microbiologist believe that heavy metals are promoting antibiotic resistance?

Because the heavy metals are present in the bacteria with antibiotic resistance. That's a correlation! While the stimulus does note that the heavy metals causally contribute to the heavy metal resistance, that doesn't relate to this separate resistance, so we can't support the causal relationship. As with any Strengthen question that has a correlation/causation flaw, we should look for answers that:
(1) Eliminate an alternative cause
(2) Shows more examples of cause and effect going together
(3) Shows a "control" of a situation without the cause and effect
(4) Explains how the causality works

Answer Explanation:
This answer establishes a control. The bacteria in this answer haven't been exposed to heavy metals and don't have antibiotic resistance. Additionally, they have been exposed to other substances in sewage ("in other respects similar"). So the answer here finds an example where essentially just the cause was removed and the effect went away.

Key Takeaway:
Correlation/causation flaws are very common in Strengthen questions. Rely on the patterns in the answer choices for these so you can get through them quickly and accurately!

Incorrect. This answer is a bit of reversed causality, which cuts against the argument instead of supporting it.

Incorrect. This answer establishes a potential alternative cause—much as exposure to heavy metals promotes heavy metal resistance, exposure to antibiotics might have caused the antibiotic resistance.

Incorrect. Without establishing anything about these other places bacteria can live—does it include high levels of heavy metals?—we can't say what effect this has on the argument.