Passage Summary: People think using peat moss is green, but it's actually bad because we're using it up too fast and it's vital for our oxygen supply.

Conclusion: Gardeners are wrong to believe that using large amounts of dried peat moss is an environmentally sound practice.

Reasoning: Sphagnum moss (the source of peat) produces more oxygen than all rain forests combined, yet the industry is harvesting it faster than it can grow back.

Analysis: To justify the conclusion that the practice is not 'environmentally sound,' we need a principle that links the premises (depletion and oxygen loss) to that specific judgment. The argument provides facts about the moss's importance and its rate of depletion but lacks a formal rule saying 'if you do X, it is not environmentally sound.' Look for a principle that states that any practice involving the unsustainable harvest of a major oxygen-producing resource is environmentally harmful.