Astrid's Friend Evan Is Taking a Psychology Course

Astrid's friend Evan is taking a psychology course. He tells her all about Sigmund Freud's psychodynamic perspective, John Watson's behavioural perspective, and Abraham Maslow's humanistic perspective. Astrid becomes frustrated, because some of the perspectives seem to say the same thing, just in different ways. "What's the point of all the different perspectives?" she asks Evan. "Why not use just one?" Evan should tell her that

A) psychology has diverse historical roots, and different groups of psychological professionals emphasize different aspects of human behaviour.
B) the problem is primarily a political one, and since psychology is a relatively new science, the politics haven't been worked out yet.
C) there's really no reason that anyone can point to; the different perspectives are just tradition, and psychology strongly values its own traditions.
D) all the different perspectives are actually subsets of mind-body dualism.
E) the different perspective are all merely of historical interest and, in fact, modern psychologists do only rely on a single perspective for research purposes.