Micah Really Liked His Mom's Homemade Apple Pie, and He

Micah really liked his mom's homemade apple pie, and he would eat a huge slice whenever she made some. When he went to visit with a friend, he tried some apple pie that the friend's brother had made, and it tasted terrible. Now Micah will only eat his mom's apple pie; if anyone else offers him apple pie he politely turns that person down. Micah's behavior toward apple pie illustrates the concept of

A) stimulus discrimination.
B) stimulus generalization.
C) noncontingent reinforcement.
D) observational learning.