Dr. Harbinger is studying a new psychotherapy treatment for depression. He carefully screens potential participants to make sure they fit strict diagnostic criteria and randomly assigns them to a treatment or control group. He is most likely conducting a(n) study.

Efficacy

Explanation: When the evaluation of a treatment or intervention is performed under well laid out and defined guidelines, such study is most likely classed as an efficacy study. Efficacy studies usually require that participants and environmental factors meet certain requirements and the risk of external or confounding variables or constraints impacting the research study is avoided or reduced to the barest minimum.

Dr. Harbinger's study as described above is most likely to be an efficacy study as it required participants to meet strict diagnostic criteria before being assigned to a group.

what are the options?

i would say b. research typically uses a variety of sources