Dr. Mary Contrary is studying the effects of the trait of agreeableness and the situation of being criticized for angry feelings. Mary gives 40 students the Niceness Inventory, and then randomly assigns half of them to receive criticism and half to receive neutral comments. Finally, she gives all of the students the Angry Mood Test (a self-report measure of current angry feelings). The critical versus neutral comments to the students are
a. manipulated dependent variable
b. measured dependent variable
c. manipulated independent variable
d. measured independent variable