Mary’s parents want her to put her books in her bookcase. At first, they praise her for putting the books together in one pile. Then they praise her for getting the books on the same side of the room as the bookcase. When she gets the books on top of the bookcase, she gets praise. Finally, her parents praise her when she puts her books in the bookcase. This is an example of     negative reinforcement     punishment     extinction     shaping     generalization