Question

why must an experiment have a control group?
a control group ensures that only the dependent variable is affecting the results of the experiment.
a control group acts as a baseline for comparison when changing the dependent variable.
a control group acts as a baseline for comparison when changing the independent variable.
a control group ensures that only the independent variable is affecting the results of the experiment.

Explanation:

A control group is unchanged while the independent variable is manipulated in the experimental group. It serves as a baseline for comparison.

Answer:

C. A control group acts as a baseline for comparison when changing the independent variable.