An experiment is defined as a

A) self-correcting process for asking questions and observing nature's answers.
B) measure of the extent to which two factors vary together.
C) research method in which an investigator manipulates one or more factors to observe the effect on some behavior or mental process.
D) technique for obtaining the self-reported attitudes or behaviors of a particular group.

Option C is the correct description of an experiment. It involves manipulating one or more factors (independent variables) in order to observe their effect on a behavior or mental process (dependent variable). This is typically done by comparing the outcomes of a group who receives the manipulation (experimental group) to a group who doesn't (control group). Option A describes the scientific method, option B describes correlation, and option D describes a survey.