Dr. Fry is doing a research study in which he takes 12-year-olds and randomly assignments to one of two groups: a group who has to read a pamphlet on STD's, and a group who has to watch a video with other adolescents who contracted STD's because of early sexual activity. He then asks them to fill out a survey to see if there is a difference in attitudes about early sexual activity that may be caused by the type of educational material they were exposed to. In this situation, which is the independent variable? the things the adolescents in the video said the type of educational material students reviewed O the responses on the survey O the age of the participants