Which of the following represents a control variable in an experiment?

A control variable in an experiment is crucial for ensuring that the results are reliable and valid. It refers to aspects of the experiment that are kept constant throughout the trial to prevent them from influencing the outcome. By maintaining these variables at stable levels, the experimenter can isolate the effect of the independent variable on the dependent variable.

Choosing the option that represents a condition kept constant highlights the fundamental principle of fair testing in scientific research. It allows researchers to make accurate comparisons and conclude that any observed changes in the dependent variable are a direct result of the manipulation of the independent variable, rather than being influenced by other factors.