Support Among people who live to the age of 100 or more, a large proportion have led "unhealthy" lives: smoking, consuming alcohol, eating fatty foods, and getting little exercise. █████ ████ ████████ █████ █████ ██ █████████ ████ ██████ ██ ██ ██████ ████ █████████████ ██████████ ██████ ███ ███████████ ████████ ██ ██████ ████ ██████
The author concludes that it’s likely people who live very long lives are genetically disposed to do so. This is because a significant proportion of people who live very long lives have led unhealthy lifestyles, which we would usually expect to shorten a person's life.
This is a phenomenon-hypothesis argument: the author observes a phenomenon, in this case the unexpected mismatch between lifespan and lifestyle, and forms a hypothesis to explain it, in this case that lifespan is likely genetically influenced. The common approaches that we can take to strengthen this type of argument include eliminating one or more competing explanations, or finding additional evidence consistent with the author's hypothesis.
The stimulus doesn't offer a whole lot of detail about how lifestyle impacts lifespan: it tells us that some factors "often" have an effect of reducing people's lifespan, but we don't know how often this happens, or how severe the reduction is likely to be. We also don't know what range of factors influence lifespan—lifestyle and genetics are the only two presented, but there could easily be more.
All of this missing information tells us that the author is making assumptions to fill in the gaps. These assumptions might be specific (for example, that genetics can have at least as great an impact on lifespan as can lifestyle) or general (for example, that there isn't a third factor other than genetics or lifestyle which neatly explains why some people live longer than others). Affirming one or more of the author's assumptions can accomplish the goals noted above, and in the process strengthen the argument.
Which one of the following, ██ █████ ████ ███████████ ███ █████████
There is some ████████ ████ █████████ █ ████████ ██████ ██ ███████ ███ ██████████ ███ ███████ ██ ██████ █████ ██████
All this tells us is that unhealthy behaviors might have different effects in combination than they do alone. But while that might modify the degree of unhealthiness in specific cases, it doesn't change that these behaviors are unhealthy overall. And even if it did, that would only weaken the argument by suggesting that an unhealthy lifestyle might not actually be so bad.
Some of the █████████████ ██████████ ██████ ███ ██ ███ █████ ██ █████ ██ ███ █████ █████ ███ ███ ██████ █████████
Like (A), all this is doing is adding nuance to the idea of an unhealthy lifestyle. We already know that a good number of long-lived people have led definitively unhealthy lives, so we're not concerned with debating that—and this doesn't provide any further support for the idea that genetics, rather than lifestyle, might be the reason for long lifespans.
Some of the █████████████ ██████████ ██████ ███ ████████ █████████ ███ █████ █████ █████ ██ █████ ██ ███████ ████████
This is basically a mirror image of (B), just swapping out some unhealthy lifestyle factors for others. And exactly like (B), it makes no difference to the argument, because the author is trying to explain how people with certifiably unhealthy lifestyles still live so long. The exact combination of factors for specific individuals isn't relevant.
Some people who ██ ███ ████ ██ ███ ███ ██ ███ ████ ████ █████████ ██████
This is almost certainly true. However, the author makes no causal claim about leading an unhealthy life and living for a long time. We're concerned with the cases where people who live unhealthy lives do live to 100, and specifically with establishing that genetics are the responsible factor. This doesn't help with that.
Answers that provide additional support for a claim that the argument doesn't need more support for.
Nearly all people ███ ████ ██ ███ ██ ████ ████ ████████ ███ ███ ████ ███████████
This strengthens by providing additional supportive evidence. If a certain trait is genetic, then we would expect it to be shared between people who share genetics—like siblings. And if an overwhelming majority of long-lived people have long-lived siblings, it's probably genetic similarities, rather than any lifestyle differences, that matter.
Presenting evidence that corroborates (in Strengthen) or conflicts (in Weaken) with the author's hypothesized explanation or the predictions that follow from that explanation.
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