A researcher wants to conduct an experiment to determine if eating a cookie before class each day improves student grades. He uses two psychology classes for the experiment, providing daily cookies to one and nothing to the other.

At the end of the semester, the researcher compares the final grades of students in the two classes. What is the independent variable for this experiment?

a. The students in the class that received cookies

b. The presence or absence of cookies

c. The students in the class that didn’t receive cookies

d. The period of the day that the two classes met

e. Semester grades