The correct answer is an experiment.
An experiment refers to an investigative study, where a researcher scientifically tests a hypothesis. Specifically, a researcher tests the effect an independent variable (manipulated variable) on the dependent variable (outcome), to investigate whether there is a causal (cause and effect) relationship between the variables. For instance, if a researcher wants to determine a cause and effect relationship between alcohol consumption and driving ability, he or she would use an experimental research study to do so.