Which tutorial method is more effective in learning calculus? Two tutorial sections of a calculus course were created where one section has graduate student tutors and the other section had faculty tutors. Students were free to sign up for either tutorial section. The final grades of the students were compared at the end of the course. Which of the following is correct?

A). The explanatory variable is the type of tutor.

B). The experimental unit is the student.

C). The response variable is the student.

D). The factor is the grade of the student.