How would a clinical psychology researcher know whether client-centered therapy is effective in treating anxiety?

A. Clients randomly assigned to be hypnotized report lower anxiety than those who are not hypnotized.

B. Clients test lower in anxiety after a reframing exercise than they did before the exercise.

C. Clients randomly assigned to be spoken to with unconditional positive regard have lower cortisol levels than those in a control group.

D. Clients who take benzodiazepines have lower heart rates than those who take a placebo.

E. Clients who engage in weekly group sessions report lower anxiety than those who have weekly solo sessions with a therapist.