Passage Summary: A lot of people who live to be 100 smoke and eat junk food, which usually kills people early, so they must have great genes keeping them alive.

Conclusion: People who live to be 100 or older are likely to have a genetic predisposition for longevity.

Reasoning: Many centenarians engage in unhealthy habits like smoking and poor diet that typically shorten lifespans, yet they still live exceptionally long lives.

Analysis: The argument assumes that if lifestyle isn't the cause of their long life—because their lifestyle is actually quite bad—then genetics must be the primary driver. To strengthen this, we should look for an answer that rules out other potential causes or further links these individuals to a genetic advantage. For example, if their siblings also lived to 100 despite similar bad habits, the genetic case becomes much stronger.