In a Study on Treatments for Anorexia, Researchers Recruited 30

In a study on treatments for anorexia, researchers recruited 30 teenage girls with anorexia. The girls were ranked by weight prior to the study. Of the heaviest three girls, one was randomly assigned to a "family" therapy, one to a "cognitive/behavioral" therapy, and one to a control group. The same was done for the next three heaviest girls, down to the three lightest girls. After five weeks of treatment, researchers weighed the participants. Researchers would like to determine which, if any, of the treatments are most effective in treating anorexia.
-If the researchers found that there were statistically significant differences in average weight across the three treatments, would they be justified in concluding that the treatments caused the changes in weights?

A) No, since we do not know which treatment was most effective.
B) No, since weight was not randomly assigned.
C) Yes, since therapy group was randomly assigned.
D) Yes, since this was an observational study.