Justify the need for a control in an experiment. use complete sentences

The control is necessary to make sure that you can tell the difference between the regular, non changed experiment, and the change that happens.
Basically, the control helps you to measure, or observe, the difference in experiments.

And example would be using pills, or flavor water, to see how it affects people. 
The control would be the group that either doesn't receive pills or water. This is basically to see how it is normally. The norm.

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