Which of the Following Is a Good Statement of a Study

Which of the following is a good statement of a study hypothesis?

A) Scores on depression will improve because of the effects of the service.
B) There is a positive relationship between scores for self-esteem and grades in school.
C) People will better understand the effects of the full moon because of the workshop they will attend on the research that has been conducted on this subject.
D) Given the importance of dysfunctional thinking on depression, cognitive behavioral therapy will prove to be effective because it addresses dysfunctional thinking about life events.