A Medical Journal Published the Results of an Experiment on Depression

A medical journal published the results of an experiment on depression. The experiment investigated the effects of a controversial new therapy for depression. Researchers measured the depression levels of 69 adult women who suffer moderate conditions of the disorder. After the therapy, the researchers again measured the women's depression levels. The differences between the the pre- and post-therapy depression levels were reported. How many levels does the treatment have in this experiment?

A) 138 (the adult women who suffer from depression measured pre- and post-therapy)
B) 2 (pre- and post-therapy)
C) 1 (therapy)
D) 69 (the adult women who suffer from depression)