The correct answer is experiment
Experiment is "a type of scientific research in which the researcher manipulates and controls one or more independent variables and observes the variation in dependent variables concurrently with the manipulation of independent variables."
The purpose of manipulating and measuring the variables in the experiment is to capture causality (relationship between cause and effect). Independent variables are responsible for possible causes, and dependent variables signal the effects. Two variables may have a very high correlation, but not necessarily one cause the other. There are three conditions for admitting causality