Final answer:
Functionalism, developed within the field of psychology, is not one of its roots but a subsequent school of thought focusing on the function of mental activities in adaptation.
Step-by-step explanation:
The roots of psychology can be traced back to several early disciplines, including psychophysics, physiology, and philosophy. These fields contributed to the development of psychology by exploring the functions and processes of the mind and body, as well as the nature of knowledge and existence. However, functionalism is not considered a root of psychology but rather a school of thought that emerged within psychology. Functionalism, developed by influential thinkers like William James, John Dewey, and Charles Sanders Peirce, was focused on how mental activities helped an organism to adapt to its environment and emphasized the purpose or function of behavior in the world. The correct answer is D) Functionalism, as it is not one of the roots of psychology but rather a result of its foundation.