Why is it important that an experiment include a control?
1. The control group always produces a positive result.
2. The control group dictates what must be done in an experiment.
3. The control group always produces a negative result.
4. A control group is required as a standard to compare with the other treatments.
5. The researcher controls some subjects in the control group but not others
4 is the correct answer.
Your teacher wants to see ":4":. However, some scientific studies do just fine without controls. I suppose you could weasel out by saying that these studies are not ":experiments":.