Your great uncle recently had a stroke, and there have been some subtle differences in his behavior. ...

Your great uncle recently had a stroke, and there have been some subtle differences in his behavior. For example, you were playing checkers, and he was doing fine. But when your checker was kinged and could therefore move according to a different set of rules, he didn't seem to be able to adjust. When you asked him if he realized what the rules said, he did, but he continued to play as if he didn't. Considering what you learned about brain areas and memory, what part of his brain would you suspect has damage?
 
  a. the hippocampus
 b. the diencephalon
 c. the prefrontal cortex
 d. the parietal lobe