A Nurse Is Designing a Study to Determine Whether a Videotape

A nurse is designing a study to determine whether a videotape or a written pamphlet is more effective in teaching young women how to perform breast self-examination (BSE) .Which of these actions would provide the best control for a mediating variable?

A) Include identical content in both BSE teaching methods
B) Exclude participants who already perform BSE on a regular basis
C) Limit the study participants to women who are heterosexual
D) Determine what breast cancer means to the individual participants