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 .
a. modeling
b. shaping
c. negative reinforcement
d. secondary learning

(B) Shaping

Explanation:

  Shaping is one of the technique that is used in the operand conditioning and the behavior shaping process in which we usually giving reward for accomplish the given task successfully.

 The shaping is also known as the procedure of the reinforcement behavior which involve the targeting behavior.

 According to the question, the given example is best illustrating the concept of shaping as polar bear is suffering from the tooth pain and veterinarian was easily able to treat the tooth problem while bear was waited for the reward.  

  Therefore, Shaping is the correct answer.