At a school there are two sections of algebra I for students in the 9th grade. The two classes have different teachers. The principal is interested in gauging the effectiveness of two different teaching methods and asks each teacher to try one of the other methods. At the end of the semester both classes are given the same test and the results are compared. In this experiment, which is the variable of interest? A. The two different math classes B. The two different teaching methods C. The two different math teachers D. The two different class test results