In an experiment, a group that serves as a standard of comparison with another group to which the control group is identical except for one factor.

• A. Control Group
• B. Hypothesis
• C. Development
• D. Tools of Science

Answer: (A)

The concept being tested is the role of a control group in an experiment. The control group serves as a standard of comparison and is kept identical to the experimental group in every way except for the one factor being tested. This setup allows any observed differences to be attributed to that specific variable, rather than to other conditions like environment or handling. Sometimes the control group may receive a placebo, or simply not receive the experimental treatment, to ensure a fair baseline. The key idea is that both groups are treated the same in all other respects so that the variable of interest is the only difference.

The other options don’t fit because they refer to different ideas: a hypothesis is a testable statement, not a group of subjects; development describes growth or change over time; and tools of science are the methods and instruments used, not a group in an experiment.