Louis needs a screwdriver to fix his remote-controlled care but he doesn't have one on hand. It does not occur to him that the dime in his pocket could serve as a makeshift substitute. This is because he is experiencing ________

a. mental set
b. prototyping
c. functional fixedness
d. an ill-defined problem

Answer: C

Rationale: This occurs when an individual encounters a potential operator, but can think of only its most obvious function.