Evaluating professors and types of variables: Weinberg, Fleisher, and Hashimoto (2007) studied almost 50,000 students' evaluations of their professors in almost 400 economics courses at The Ohio State University over a 10-year period. One finding was that students' ratings of their professors were predictive of grades in the class for which the professor was evaluated. How would you classify the independent and dependent variables in this study?a. Professors' gender; levels: male and femaleb. Professors' seniority; levels: graduate student, non-tenure-track and tenure-trackc. Students' evaluationsd. Students' GPAs