At the National Zoological Park in Washington, D.C., a polar bear suffered a broken tooth, and keepers needed a safe way of treating the problem. The bear was rewarded first for sticking its nose through a slot in the cage door, then for allowing a keeper to lift its lip and touch its teeth. Finally, a veterinarian was able to treat the damaged tooth while the bear waited placidly for its familiar reward. This is an example of ________.
◦ secondary learning
◦ modeling
◦ negative reinforcement
◦ observational learning
◦ shaping