Figure: a Researcher Was Interested in the Effects of Arousal and and Personality

Multiple Choice

Figure:
A researcher was interested in the effects of arousal and personality on individuals' GRE test performance.The personality variable he examined was individuals' level of introversion-extraversion.Based on questionnaire responses,each participant was classified as an "extravert" or an "introvert." The researcher manipulated arousal level by giving caffeine to participants prior to administering a practice GRE test.Participants were randomly assigned to a high-caffeine condition,a medium-caffeine condition,or the no-caffeine conditions.All participants then completed a practice version of the quantitative portion of the GRE.
Suppose the researcher observed the following means for each group:
-The random groups independent variable in this experiment is

A) scores on the quantitative portion of the GRE test.
B) participants who volunteered to participate in the experiment.
C) level of arousal: high-caffeine,medium-caffeine,or no-caffeine.
D) participants' personality: introversion or extraversion.