Dr. Smith examined the effect of caffeine on psychology exam scores. Half of the participants in her study were assigned to drink decaffeinated coffee and half of them were given caffeinated coffee. She then had them take a psychology exam and measured the number of answers they got correct. What was the dependent variable in this study?

a) The type of coffee consumed.
b) The participants' scores on the psychology exam.
c) The number of participants.
d) The time it took for participants to drink the coffee