Definition: In this task, you are given a multiple-choice question about healthcare. Answer the question based on your information and classify your answers into '1', '2', '3', and '4'.
Input: Question: What specific procedure of the experimental strategy makes it the most appropriate to test hypotheses of causality? : 
 Options:  <1> The representative sampling of the participants. <2> The manipulation of the independent variable with control of possible strange variables. <3> The realization of the study in real contexts with natural groups. <4> The identification of possible predictor variables through the retrospective analysis of the study phenomenon. <5> The application of statistical techniques for the analysis of data.
