easy · GRE Verbal
**Potted houseplants meaningfully purify the air inside homes** — so runs a claim repeated on countless gardening blogs and product labels. The claim traces back to a laboratory study in which plants sealed inside small chambers removed airborne toxins. Yet a typical living room is not a sealed chamber: its air is exchanged with outdoor air several times a day through leaks, vents, and open doors. Researchers who scaled the chamber results to realistic household conditions calculated that a homeowner would need hundreds of plants per square meter to match the cleaning effect of ordinary ventilation. **Houseplant owners should therefore expect essentially no measurable improvement in their air quality from their plants.**
In the argument above, the two portions in boldface play which of the following roles?
- The first is a claim that the argument disputes; the second is the main conclusion of the argument.
- The first is the main conclusion of the argument; the second is evidence offered in support of that conclusion.
- The first is evidence supporting the argument's conclusion; the second is a restatement of that conclusion.
- The first is a claim that the argument disputes; the second is evidence offered against that disputed claim.
- The first is a concession the argument accepts as true; the second is a prediction that rests on that concession.
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