In attempting to solve the "nine dot problem" few individuals attempt to draw a line outside the imaginary boundary surrounding the nine dots.This is not a rule associated with the problem but is imposed by the problem solver.What is this an example of

A)  trial-and-error learning 
B)  functional fixedness 
C)  mental set 
D)  unnecessary constraints

Mental Set

A framework of thinking, including habits, attitudes, and experiences, that shapes how an individual perceives and responds to situations.

Functional Fixedness

A mental bias that restricts an individual to employing an item solely in its conventional use, obstructing the resolution of problems.

Nine Dot Problem

A puzzle that challenges individuals to connect nine dots arranged in a square grid using four straight lines or fewer, without lifting the pen from the paper.