What is the main purpose of controlled variables in an experiment?
they compare the findings of one experiment to another.
they produce reliable results without repeating the experiment.
they investigators practice measuring without affecting the results of the experiment.
they ensure that changes in the independent variable are affecting the dependent variable.

They help ensure that changes in the independent variable are affecting the dependent variable.

A controlled variable can be defined as a variable in a scientific experiment. It is a variable that is kept constant and remains unchanged throughout the course of the investigation. It is kept constant to determine the relative relationship between the dependent and independent variables. The changes in the independent variable can be observed or measured in order to determine the effect on the dependent variable.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

i thinking chemical change