According to the Text, Why Are So Many Treatment Approaches

According to the text, why are so many treatment approaches effective in the treatment of unipolar depression?

A) Each of the treatments employs the same underlying principles.
B) Multiple, interacting factors contribute to unipolar depression, and correcting dysfunction in one area helps improve functioning in other areas as well.
C) Unipolar depression is, overall, one of the most straightforward and simplest psychological disorders to treat.
D) Numerous highly accurate assessment tools available to identify the cause of unipolar depression and, in turn, customize treatment to the individual.