Final answer:
The control group in an experiment provides a reference for determining the impact of the independent variable, ensuring observed effects can be attributed to the experimental manipulation.
Step-by-step explanation:
The importance of including a control group in an experiment is to provide a reference point that can be used to determine if the changes observed in the experimental group are due to the variable being tested or some other factor. Among the given options, the correct answer is: C) To provide a reference for determining reasonable outcomes. A control group allows for a comparison between groups that differ in only one independent variable, ensuring that any observed effects can be attributed to the experimental manipulation and not to other variables.
A controlled experiment is one in which a researcher compares an experimental group to a control group, and all conditions are kept the same except for the independent variable being tested. This design helps to ensure that the results are due to the experimental manipulation rather than chance or outside influences. Experimental controls are essential in the scientific method as they help in determining the efficacy of treatments, the accuracy of the hypothesis, and the overall validity of the experiment.