C. A controlled experiment is an experiment in which only one variable is changed at a time. Why is it important to do a controlled experiment in order to determine how a
variable, such as water, light, or temperature, affects seed germination rates?

Conducting a controlled experiment is necessary to determine how a variable affects seed germination rates because it decreases the chances of other factors impacting the dependent variable. Only changing one variable at a time and keeping the others controlled allows the experimenter to accurately identify the effects of that one independent variable.