PrepTest 132

Incorrect. If anything, this suggests that some of those unhealthy people didn't have good genes but managed to balance their unhealthiness somehow, thus cutting against the argument.

Incorrect. The argument already accounts for long-lived people having some, all, or none ("large proportion" isn't everyone), so there being a group that doesn't touch booze or alcohol but does eat fast food without exercising doesn't add to the argument. Also, note that if this answer were correct, (C) would be as well, so both can be ruled out.

Incorrect. The argument already accounts for long-lived people having some, all, or none ("large proportion" isn't everyone), so there being a group that doesn't touch booze or alcohol but does eat fast food without exercising doesn't add to the argument. Note that if this answer were correct, (B) would be as well, so both can be ruled out.

Incorrect. This information is already included in the argument—"such behavior often leads to shortened life spans."

Correct. Argument or Facts:
Argument

Valid or Flawed:
Flawed

Question Type:
Strengthen

Stimulus Summary:
Many long-lived people led unhealthy lives that often lead to an early grave, so these people must have good genes.

Answer Anticipation:
Strengthen questions frequently feature correlation/causation flaws, and this argument does have causality buried in its conclusion—it's essentially saying that the genes (not lifestyle) is causing these individuals to have a long life. However, this question is, interestingly, based on using a correlation to rule out an alternative cause—lifestyle. These long-lives are correlated with unhealthy habits—unhealthy habits that have been established in the premises to cause shortened lifespans.

So the argument doesn't have a straightforward correlation/causation flaw, but it does use a correlation to rule out one cause and then jump to another. So it is committing a correlation/causation flaw in a roundabout way. As such, we can look for answers that fall into the common categories:

(1) Eliminate alternative causes (in particular, provide more evidence against lifestyle causes)
(2) Find more examples of cause and effect going together
(3) Find a control—people without good genes dying young
(4) Explain the causality, maybe with an answer about how certain longevity genes also increase the desire for unhealthy things

Answer Explanation:
While this answer doesn't discuss the habits of these siblings, it Must Be True that these siblings have some shared genes, and so these genes being correlated with more long-lived individuals strengthens the causal relationship concluded in the argument. This answer falls into the second common category of answers—more examples of cause and effect going together.

Key Takeaway:
Strengthen questions very frequently feature correlation/causation flaws. Whenever you see a causal conclusion in this question type, check to see if it's based in any way on a correlation. When it is, start looking for an answer that falls into one of the common categories.