Passage Summary: Kidney stones are made of concentrated calcium, so doctors used to think eating less calcium would help; however, it turns out that eating more calcium actually lowers the risk of getting more stones.

Reasoning: No reasoning (Fact Set).

Analysis: The paradox lies in the fact that while kidney stones are made of calcium, increasing calcium intake actually prevents them. To resolve this, we need a reason why dietary calcium doesn't end up as concentrated calcium in the kidneys. Perhaps calcium in the digestive tract prevents other stone-forming substances from being absorbed into the bloodstream. Look for an answer that explains how dietary calcium acts as a preventative agent rather than a building block for stones.