According to the "Functional" Perspective Beginning in the 1920s, It

According to the "functional" perspective beginning in the 1920s, it is the ______.

A) interaction between the client and the worker that accounts for the process of change
B) interaction among different professions that accounts for the process of change
C) interaction between the client and the environment that accounts for the process of change
D) interaction among different systems that that accounts for the process of change