Today there are many alternative approaches to treatment, including client-centred therapy, cognitive therapy, behaviour therapy and biomedical therapies. This wide range of alternatives illustrates that

A) behaviour is determined by multiple causes.
B) psychology evolves in a socio-historical context.
C) psychology is theoretically diverse.
D) heredity and environment jointly influence behaviour.

The fact that there are multiple alternative approaches to treatment illustrates that psychology is theoretically diverse, as different theories and perspectives have led to the development of different approaches. A and D may also be true, but they are not directly relevant to the question of why there are multiple alternative approaches to treatment. B is not a direct explanation for this phenomenon either, although it is true that psychology is shaped by social and historical factors.