Amixed economy based upon: a) strict laissez faire capitalism b) private enterprise and governmental regulations coexist c) government control and regulation of private industry d) privatization and nationalization

Martha participates in a research study in order to receive extra credit for her psychology class. when she arrives in the research office she is given a can of what looks and tastes like beer, but which actually contains no alcohol. in the adjoining room martha's classmate karen is also participating in the study. karen receives a can of alcoholic beer. if the experiment was designed to test the effects of alcohol on concentration, then who is exposed to the independent variable?