What is a example of a control group? ?

A control is your group that you do not subject to the experimental protocol. For example, if you wanted to test to see if some drug lowered blood pressure and you just gave some people the drug and measured their blood pressure, how do you know if just taking a pill and thinking it could help was enough to have an effect? The control group that gets an inert pill gives you something to compare your results to to ensure that any effect is from the drug itself.