Functionalism is the . . . . . . . . school of thought in Psychology.

Functionalism is considered the first school of thought in psychology. It emerged as a distinct approach in the late 19th and early 20th centuries, particularly associated with the work of William James. Functionalism focused on the function of mental processes, particularly in how they help individuals adapt to their environment. This perspective was interested in understanding the purpose or function of psychological processes and how they contribute to an individual's survival and well-being.

The other options are not accurate:
Option A: Second is not correct because functionalism is the first school of thought in psychology.
Option C: Third and Option D: Fourth are not correct either. There is no third or fourth school of thought called "Functionalism" in the history of psychology.

So, the correct answer is Option B: First, as functionalism is the initial school of thought in psychology that emerged as a reaction to structuralism.