There is reference in the graph to race. But race is limited to African-American and Caucasian. This could be a problem in that we can't tell what was included in Caucasian. This would certainly seem to indicate that the categories might not have been mutually exclusive and exhaustive. Race was one of the variables.
Aggression seems to be measured along the x-axis.
Aggression to the left, over-protection to the right, judging by the lables on the graph. Aggression was one of the variables. Performance seems to measured along the y-axis, with optimal performance at the top, minimal performance at the base line. Performance seems to be one of the variables. All of the above would be the best answer choice, since the graph indicates that all of the above variables were measured.