You Are Considering the "Dress Well, Test Well" Theory, Which

You are considering the "dress well, test well" theory, which argues that you perform better on exams when you dress nicely than you do when you wear sweatpants. If you want to test this theory over the course of the semester, which of the following would be an endogenous factor in your experiment?

A) your innate ability in the subject
B) the difficulty of the exam
C) the relative mix of multiple-choice and
D) your clothing choice for the exam
E) the amount of time you spend studying for the exam