Answer: Spontaneous recovery likely occurred, and the dog salivated in response to the triangle
Explanation:
Spontaneous recovery is the reappearance of the conditioned response when a rest period has taken place or when there's a period of lessened response.
In this case, since the researchers put the dog back in his cage for three hours after which the dog went through the conditioning process again after the three hours, then there'll be a spontaneous recovery.