Passage Summary: The nylon industry says nylon is natural because it's made from things like air and old plants (oil), and since those things are natural, nylon must be too.

Conclusion: Nylon should be considered a natural substance rather than a synthetic one.

Reasoning: Nylon is made from petroleum (which comes from ancient plants) and nitrogen from the atmosphere, both of which are natural sources.

Analysis: The argument relies on a 'part-to-whole' or 'origin-to-product' logic. It assumes that if the constituent parts of a product are natural, then the final product itself must be classified as natural. To justify this, we need a principle that explicitly bridges that gap. Look for an answer that states something like: 'Any product whose primary components are derived from natural sources is itself a natural product.'