Stuart Hates Passing the Neighbours' House on His Walk Home

Stuart hates passing the neighbours' house on his walk home from school because the bulldog there barks at him. Because of this, Stuart became anxious around all dogs; however, his family recently adopted a Labrador retriever. The dog is very gentle and never barks at Stuart, and now Stuart is anxious only around the bulldog down the street. Stuart has learned to

A) generalize.
B) discriminate.
C) condition the bulldog.
D) condition the Labrador retriever.