Suppose That Your Professor Needs Volunteers for a Psychology Study

Suppose that your professor needs volunteers for a psychology study.She will be most successful in getting students who volunteer to actually show up for the study if she

A) passes around a sign-up sheet with the time and place of the study and asks students who want to volunteer to sign their name.
B) writes on the board the time and place of the study for those who want to volunteer.
C) passes a flyer with the time and place of the study for those who want to volunteer.
D) has a research assistant stand up in front of the class and announce the time and place of the study for those who want to volunteer.