RESEARCH STUDY 3.1: Anderson is reading his morning paper and sees the following headline: "Men Should Avoid Rock Music When Playing Board Games." (This headline is based on a study conducted by Fancourt, Burton, & Williamon, 2016.) In the study, men and women played the game "Operation" when listening to different types of music. Male participants performed worse when listening to AC/DC than when listening to Mozart, but female participants’ performance did not differ based on music. How many variables are included in this study? Group of answer choices