easy · Enhanced ACT science

A scientist hypothesizes that higher levels of nitrogen in soil lead to taller sunflowers. She compares sunflowers in soil with 5% nitrogen to those in soil with 10% nitrogen. However, the 10% nitrogen group was also watered twice as often.

Why does this design fail to support the hypothesis?

  1. The nitrogen levels are not extreme enough
  2. The study should have used 0% nitrogen
  3. Water frequency has become a confounder
  4. Because nitrogen is a difficult factor to add

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