What’s a control group?

Question: What’s a control group?

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

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