Explain the Matched-Pairs Design

Explain the Matched-Pairs Design
-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 95 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. What is the treatment in this experiment

A) the therapy
B) the 95 adult women who suffer from depression
C) the disorder (depression or no depression)
D) the differences between the the pre- and post-therapy depression levels