Which statement about mound builder works is true? earthen mounds were created for children to play on. bowls shaped like animals were made of stone. portraits were made of solid gold and painted with bright colors

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?