Question

which option is the control in an experiment?

a. water, BTB, covered in foil with no Elodea placed under a strong light source
b. water, BTB, Elodea covered in foil placed under a strong light source
c. water, BTB, Elodea placed under a strong light source
d. water and Elodea
GPT-4o mini
In an experiment, the control is the variable that is kept constant to provide a baseline for comparison. Typically, the control does not have the experimental treatment applied to it.

In this case, option **a** (water, BTB, covered in foil with no Elodea placed under a strong light source) serves as the control because it does not contain the Elodea. This means it will allow you to compare the effects of the Elodea on the system when it is included (options b and c) against a scenario where it is not present.

Thus, the correct answer is:

**a. water, BTB, covered in foil with no Elodea placed under a strong light source**.

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