Dee Dee Taught His Dog Bosco to Roll Over Whenever

Dee Dee taught his dog Bosco to roll over whenever he heard the command "Spin!" After a while Dee Dee got bored with the trick,and allowed Bosco's behavior to extinguish.However,while watching Jeopardy! several months later,Dee Dee got excited by the answer "Clothes in a dryer" and shouted out "What is 'spin?!'" at which point Bosco flipped around like a circus performer.Which principle of classical conditioning does this example illustrate?

A) spontaneous recovery
B) higher-order conditioning
C) extinction
D) stimulus generalization