Perry Is Trying to Solve the Following Riddle: "What Creature

Multiple Choice

Perry is trying to solve the following riddle: "What creature walks first on four legs, then two, then three?" He repeatedly tries to think of an animal that might walk on three legs, but he can only think of animals that walk on either two or four legs. Finally, he is told the correct answer: a human being, who crawls, then walks, then walks with a cane. Which one of the following is the most likely explanation of Perry's difficulty?

A) He has encoded the problem with too narrow a definition of "legs."
B) He doesn't have enough working memory capacity.
C) He doesn't have a sufficient knowledge base.
D) He is suffering from functional fixedness.