Many businesses and organizations insist that official communications use professional-looking fonts, such as Times New Roman. Fonts characterized as less professional, such as Comic Sans, should be avoided. A student would like to determine if font choice makes a difference in the average grade on a typed response in English classes. There are currently four English classes available from which the student can collect data, and each class has a similar writing assignment. At the start of the assignment, students are randomly assigned a font, either Times New Roman or Comic Sans, and then complete the assignment. The teachers grade the assignments, and the mean grade for each font is found. What is the response variable in this experiment?

the font used by each student
the teachers grading the responses
the grade received on each assignment
the length of the student response on the assignment