Problem: A psychologist is interested in whether the title of an expert impacts people's mask-wearing behaviors. Ten individuals were given a conference on why and how to wear a mask by a professor of medicine, eight individuals were given the same conference by a medical school student, and 11 participants were given the same conference by a school counselor. After the conference, all participants were given a self-report questionnaire including questions about the effectiveness of the conference and if their behavior could change as a result. Based on the information above, what is the alternative hypothesis?
A. At least one mean is different.
B. The professor's conference will be more effective than the others.
C. The professor's conference will be more effective than the medical student's conference.
D. The professor's conference will be more effective than the school counsellor's conference.