medium · SAT Reading & Writing

In a series of experiments, researchers found that soil samples treated with a specific organic compost retained significantly more moisture than untreated samples did. While the exact mechanism is not yet fully understood, the researchers believe the compost encourages the growth of beneficial fungi that help hold water in the soil. Which choice most logically completes the text?

1. Soil moisture levels are likely influenced by the presence of certain organic materials.
2. Untreated soil samples are completely incapable of retaining any moisture.
3. The researchers have proven that fungi are responsible for all water retention in soil.
4. The mechanism by which the compost affects moisture retention has not yet been fully established.

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