Mr. Greenjeans needs a control group for comparison.
How do we know that the fertilizer had any impact on growth since Mr. Greenjeans has no control group for comparison? He must know how the pumpkins will grow without any fertilizer as well. The control group gives us a way to compare the experimental groups to help form more valid conclusions.
A rock made out of shells and corals cemented together is called a limestone.
A rock is a naturally occurring solid substance composed of one or more minerals or mineraloids.
Therefore, a limestone is a rock formed by the cementation of shells and corals.
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