Controlled experiments (article) | Khan Academy
https://www.khanacademy.org/science/biology/intro-to-biology/science-of-biology/a/experiments-and-observations
WEBWhen possible, scientists test their hypotheses using controlled experiments. A controlled experiment is a scientific test done under controlled conditions, meaning that just one (or a few) factors are changed at a time, while all others are kept constant. We'll look closely at controlled experiments in the next section.
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