Explain the Matched-Pairs Design

Explain the Matched-Pairs Design
-A medical journal published the results of an experiment on insomnia. The experiment investigated the effects of a controversial new therapy for insomnia. Researchers measured the insomnia levels of 48 adult women who suffer moderate conditions of the disorder. After the therapy, the researchers again measured the women s insomnia levels. The differences between the the pre- and post-therapy insomnia levels were reported. How many levels does the treatment have in this experiment

A) 2 (pre- and post-therapy)
B) 1 (therapy)
C) 48 (the adult women who suffer from insomnia)
D) 96 (the adult women who suffer from insomnia measured pre- and post-therapy)