Control groups are used in scientific experiments because they
A. are easily identified by the experimenter during the investigation.
B. are cheap and relatively easy to maintain throughout the experiment.
C. prevent data collection from being contaminated by other variables.
D. provide a standard of comparison with other data collected.
It prevents other variables such as independent variables and extraneous variables from affecting the validity of results. It also makes it easier to compare results when variables are changed.
