How does a control group function in an experiment?

Question: How does a control group function in an experiment?

• It’s a group separated from the rest of the experiment but are still included in the test.
• It’s a group separated from the rest of the experiment.
• It’s a group included with the experiment but are still partialy separated from the experiment.
• It’s a group included with the experiment.

The right answer was: It’s a group separated from the rest of the experiment.