After Exposure to Thirty Minutes of Sexually Explicit Film, or Erotic

Multiple Choice

After exposure to thirty minutes of sexually explicit film, or erotic but not sexually explicit film, sexual arousal is measured in female and male subjects with a penile strain gauge or a vaginal photoplethysmograph. What is the independent variable in this study?

A) Sexually explicit films
B) The penile strain gauge or vaginal photoplethysmograph
C) Gender
D) Amount of sexual arousal