In non-experimental research, what is the primary focus of the investigator?

Given below are two statements: Statement I: An operational definition translates a vague construct into measurable and observable terms for the purpose of a specific research study. Statement II: A moderator variable is a type of extraneous variable that the researcher fails to control, thereby providing an alternative explanation for the results. In the light of the above statements, choose the correct answer from the options given below:

The variable manipulated by the experimenter in an experiment is called the ________ variable.