Control groups are used in experiments in order to A Control the effects of outside variables on the outcome. B Control the subjects of a study to ensure that all participate equally. C Guarantee that someone other than the investigators, who have a vested interest in the outcome, controls how the experiment is conducted. D Achieve a proper and uniform level of randomization. E Increase the variability in response variable.

A). Control the effects of outside variables on the outcome

Step-by-step explanation:

A control group may be defined as the group that keeps separated or isolated from the rest of the samples of the experiment. This is done because the independent variable that are being tested are not able to influence the results. It is an observation or experiment designed to reduce the effects of the variables other than independent variable. It  isolates the effects of the independent variable on the experiment and increases reliability of the results. Thus it controls the effects of the outside variables on the results of the experiments.

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step-by-step explanation:

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