The correct answer is the experiment.
An experiment or experimental design in research studies refers to when a researcher manipulates and controls a variable (known as an independent variable) in order to determine its effect on other variables. In this instance, a researcher could assess whether athletic performance is boosted by drinking soda with caffeine in it by providing some athletes in the research study with a caffeinated soda and the remaining athletes with non-caffeinated soda. After this, the researcher can then find out whether the athletes who consumed the caffeinated soda had an improved performance compared to the participants who consumed non-caffeinated soda.
